xtensa: fix high memory/reserved memory collision

[cris-mirror.git] / arch / x86 / xen / mmu_pv.c

/*
 * Xen mmu operations
 *
 * This file contains the various mmu fetch and update operations.
 * The most important job they must perform is the mapping between the
 * domain's pfn and the overall machine mfns.
 *
 * Xen allows guests to directly update the pagetable, in a controlled
 * fashion.  In other words, the guest modifies the same pagetable
 * that the CPU actually uses, which eliminates the overhead of having
 * a separate shadow pagetable.
 *
 * In order to allow this, it falls on the guest domain to map its
 * notion of a "physical" pfn - which is just a domain-local linear
 * address - into a real "machine address" which the CPU's MMU can
 * use.
 *
 * A pgd_t/pmd_t/pte_t will typically contain an mfn, and so can be
 * inserted directly into the pagetable.  When creating a new
 * pte/pmd/pgd, it converts the passed pfn into an mfn.  Conversely,
 * when reading the content back with __(pgd|pmd|pte)_val, it converts
 * the mfn back into a pfn.
 *
 * The other constraint is that all pages which make up a pagetable
 * must be mapped read-only in the guest.  This prevents uncontrolled
 * guest updates to the pagetable.  Xen strictly enforces this, and
 * will disallow any pagetable update which will end up mapping a
 * pagetable page RW, and will disallow using any writable page as a
 * pagetable.
 *
 * Naively, when loading %cr3 with the base of a new pagetable, Xen
 * would need to validate the whole pagetable before going on.
 * Naturally, this is quite slow.  The solution is to "pin" a
 * pagetable, which enforces all the constraints on the pagetable even
 * when it is not actively in use.  This menas that Xen can be assured
 * that it is still valid when you do load it into %cr3, and doesn't
 * need to revalidate it.
 *
 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
 */
#include <linux/sched/mm.h>
#include <linux/highmem.h>
#include <linux/debugfs.h>
#include <linux/bug.h>
#include <linux/vmalloc.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/seq_file.h>
#include <linux/crash_dump.h>
#ifdef CONFIG_KEXEC_CORE
#include <linux/kexec.h>
#endif

#include <trace/events/xen.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/fixmap.h>
#include <asm/mmu_context.h>
#include <asm/setup.h>
#include <asm/paravirt.h>
#include <asm/e820/api.h>
#include <asm/linkage.h>
#include <asm/page.h>
#include <asm/init.h>
#include <asm/pat.h>
#include <asm/smp.h>

#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>

#include <xen/xen.h>
#include <xen/page.h>
#include <xen/interface/xen.h>
#include <xen/interface/hvm/hvm_op.h>
#include <xen/interface/version.h>
#include <xen/interface/memory.h>
#include <xen/hvc-console.h>

#include "multicalls.h"
#include "mmu.h"
#include "debugfs.h"

#ifdef CONFIG_X86_32
/*
 * Identity map, in addition to plain kernel map.  This needs to be
 * large enough to allocate page table pages to allocate the rest.
 * Each page can map 2MB.
 */
#define LEVEL1_IDENT_ENTRIES    (PTRS_PER_PTE * 4)
static RESERVE_BRK_ARRAY(pte_t, level1_ident_pgt, LEVEL1_IDENT_ENTRIES);
#endif
#ifdef CONFIG_X86_64
/* l3 pud for userspace vsyscall mapping */
static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss;
#endif /* CONFIG_X86_64 */

/*
 * Note about cr3 (pagetable base) values:
 *
 * xen_cr3 contains the current logical cr3 value; it contains the
 * last set cr3.  This may not be the current effective cr3, because
 * its update may be being lazily deferred.  However, a vcpu looking
 * at its own cr3 can use this value knowing that it everything will
 * be self-consistent.
 *
 * xen_current_cr3 contains the actual vcpu cr3; it is set once the
 * hypercall to set the vcpu cr3 is complete (so it may be a little
 * out of date, but it will never be set early).  If one vcpu is
 * looking at another vcpu's cr3 value, it should use this variable.
 */
DEFINE_PER_CPU(unsigned long, xen_cr3);  /* cr3 stored as physaddr */
DEFINE_PER_CPU(unsigned long, xen_current_cr3);  /* actual vcpu cr3 */

static phys_addr_t xen_pt_base, xen_pt_size __initdata;

/*
 * Just beyond the highest usermode address.  STACK_TOP_MAX has a
 * redzone above it, so round it up to a PGD boundary.
 */
#define USER_LIMIT      ((STACK_TOP_MAX + PGDIR_SIZE - 1) & PGDIR_MASK)

void make_lowmem_page_readonly(void *vaddr)
{
        pte_t *pte, ptev;
        unsigned long address = (unsigned long)vaddr;
        unsigned int level;

        pte = lookup_address(address, &level);
        if (pte == NULL)
                return;         /* vaddr missing */

        ptev = pte_wrprotect(*pte);

        if (HYPERVISOR_update_va_mapping(address, ptev, 0))
                BUG();
}

void make_lowmem_page_readwrite(void *vaddr)
{
        pte_t *pte, ptev;
        unsigned long address = (unsigned long)vaddr;
        unsigned int level;

        pte = lookup_address(address, &level);
        if (pte == NULL)
                return;         /* vaddr missing */

        ptev = pte_mkwrite(*pte);

        if (HYPERVISOR_update_va_mapping(address, ptev, 0))
                BUG();
}


static bool xen_page_pinned(void *ptr)
{
        struct page *page = virt_to_page(ptr);

        return PagePinned(page);
}

static void xen_extend_mmu_update(const struct mmu_update *update)
{
        struct multicall_space mcs;
        struct mmu_update *u;

        mcs = xen_mc_extend_args(__HYPERVISOR_mmu_update, sizeof(*u));

        if (mcs.mc != NULL) {
                mcs.mc->args[1]++;
        } else {
                mcs = __xen_mc_entry(sizeof(*u));
                MULTI_mmu_update(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
        }

        u = mcs.args;
        *u = *update;
}

static void xen_extend_mmuext_op(const struct mmuext_op *op)
{
        struct multicall_space mcs;
        struct mmuext_op *u;

        mcs = xen_mc_extend_args(__HYPERVISOR_mmuext_op, sizeof(*u));

        if (mcs.mc != NULL) {
                mcs.mc->args[1]++;
        } else {
                mcs = __xen_mc_entry(sizeof(*u));
                MULTI_mmuext_op(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
        }

        u = mcs.args;
        *u = *op;
}

static void xen_set_pmd_hyper(pmd_t *ptr, pmd_t val)
{
        struct mmu_update u;

        preempt_disable();

        xen_mc_batch();

        /* ptr may be ioremapped for 64-bit pagetable setup */
        u.ptr = arbitrary_virt_to_machine(ptr).maddr;
        u.val = pmd_val_ma(val);
        xen_extend_mmu_update(&u);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_set_pmd(pmd_t *ptr, pmd_t val)
{
        trace_xen_mmu_set_pmd(ptr, val);

        /* If page is not pinned, we can just update the entry
           directly */
        if (!xen_page_pinned(ptr)) {
                *ptr = val;
                return;
        }

        xen_set_pmd_hyper(ptr, val);
}

/*
 * Associate a virtual page frame with a given physical page frame
 * and protection flags for that frame.
 */
void set_pte_mfn(unsigned long vaddr, unsigned long mfn, pgprot_t flags)
{
        set_pte_vaddr(vaddr, mfn_pte(mfn, flags));
}

static bool xen_batched_set_pte(pte_t *ptep, pte_t pteval)
{
        struct mmu_update u;

        if (paravirt_get_lazy_mode() != PARAVIRT_LAZY_MMU)
                return false;

        xen_mc_batch();

        u.ptr = virt_to_machine(ptep).maddr | MMU_NORMAL_PT_UPDATE;
        u.val = pte_val_ma(pteval);
        xen_extend_mmu_update(&u);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        return true;
}

static inline void __xen_set_pte(pte_t *ptep, pte_t pteval)
{
        if (!xen_batched_set_pte(ptep, pteval)) {
                /*
                 * Could call native_set_pte() here and trap and
                 * emulate the PTE write but with 32-bit guests this
                 * needs two traps (one for each of the two 32-bit
                 * words in the PTE) so do one hypercall directly
                 * instead.
                 */
                struct mmu_update u;

                u.ptr = virt_to_machine(ptep).maddr | MMU_NORMAL_PT_UPDATE;
                u.val = pte_val_ma(pteval);
                HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF);
        }
}

static void xen_set_pte(pte_t *ptep, pte_t pteval)
{
        trace_xen_mmu_set_pte(ptep, pteval);
        __xen_set_pte(ptep, pteval);
}

static void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
                    pte_t *ptep, pte_t pteval)
{
        trace_xen_mmu_set_pte_at(mm, addr, ptep, pteval);
        __xen_set_pte(ptep, pteval);
}

pte_t xen_ptep_modify_prot_start(struct mm_struct *mm,
                                 unsigned long addr, pte_t *ptep)
{
        /* Just return the pte as-is.  We preserve the bits on commit */
        trace_xen_mmu_ptep_modify_prot_start(mm, addr, ptep, *ptep);
        return *ptep;
}

void xen_ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
                                 pte_t *ptep, pte_t pte)
{
        struct mmu_update u;

        trace_xen_mmu_ptep_modify_prot_commit(mm, addr, ptep, pte);
        xen_mc_batch();

        u.ptr = virt_to_machine(ptep).maddr | MMU_PT_UPDATE_PRESERVE_AD;
        u.val = pte_val_ma(pte);
        xen_extend_mmu_update(&u);

        xen_mc_issue(PARAVIRT_LAZY_MMU);
}

/* Assume pteval_t is equivalent to all the other *val_t types. */
static pteval_t pte_mfn_to_pfn(pteval_t val)
{
        if (val & _PAGE_PRESENT) {
                unsigned long mfn = (val & XEN_PTE_MFN_MASK) >> PAGE_SHIFT;
                unsigned long pfn = mfn_to_pfn(mfn);

                pteval_t flags = val & PTE_FLAGS_MASK;
                if (unlikely(pfn == ~0))
                        val = flags & ~_PAGE_PRESENT;
                else
                        val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
        }

        return val;
}

static pteval_t pte_pfn_to_mfn(pteval_t val)
{
        if (val & _PAGE_PRESENT) {
                unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                pteval_t flags = val & PTE_FLAGS_MASK;
                unsigned long mfn;

                mfn = __pfn_to_mfn(pfn);

                /*
                 * If there's no mfn for the pfn, then just create an
                 * empty non-present pte.  Unfortunately this loses
                 * information about the original pfn, so
                 * pte_mfn_to_pfn is asymmetric.
                 */
                if (unlikely(mfn == INVALID_P2M_ENTRY)) {
                        mfn = 0;
                        flags = 0;
                } else
                        mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
                val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
        }

        return val;
}

__visible pteval_t xen_pte_val(pte_t pte)
{
        pteval_t pteval = pte.pte;

        return pte_mfn_to_pfn(pteval);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);

__visible pgdval_t xen_pgd_val(pgd_t pgd)
{
        return pte_mfn_to_pfn(pgd.pgd);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);

__visible pte_t xen_make_pte(pteval_t pte)
{
        pte = pte_pfn_to_mfn(pte);

        return native_make_pte(pte);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte);

__visible pgd_t xen_make_pgd(pgdval_t pgd)
{
        pgd = pte_pfn_to_mfn(pgd);
        return native_make_pgd(pgd);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_make_pgd);

__visible pmdval_t xen_pmd_val(pmd_t pmd)
{
        return pte_mfn_to_pfn(pmd.pmd);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pmd_val);

static void xen_set_pud_hyper(pud_t *ptr, pud_t val)
{
        struct mmu_update u;

        preempt_disable();

        xen_mc_batch();

        /* ptr may be ioremapped for 64-bit pagetable setup */
        u.ptr = arbitrary_virt_to_machine(ptr).maddr;
        u.val = pud_val_ma(val);
        xen_extend_mmu_update(&u);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_set_pud(pud_t *ptr, pud_t val)
{
        trace_xen_mmu_set_pud(ptr, val);

        /* If page is not pinned, we can just update the entry
           directly */
        if (!xen_page_pinned(ptr)) {
                *ptr = val;
                return;
        }

        xen_set_pud_hyper(ptr, val);
}

#ifdef CONFIG_X86_PAE
static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
{
        trace_xen_mmu_set_pte_atomic(ptep, pte);
        set_64bit((u64 *)ptep, native_pte_val(pte));
}

static void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
        trace_xen_mmu_pte_clear(mm, addr, ptep);
        if (!xen_batched_set_pte(ptep, native_make_pte(0)))
                native_pte_clear(mm, addr, ptep);
}

static void xen_pmd_clear(pmd_t *pmdp)
{
        trace_xen_mmu_pmd_clear(pmdp);
        set_pmd(pmdp, __pmd(0));
}
#endif  /* CONFIG_X86_PAE */

__visible pmd_t xen_make_pmd(pmdval_t pmd)
{
        pmd = pte_pfn_to_mfn(pmd);
        return native_make_pmd(pmd);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_make_pmd);

#ifdef CONFIG_X86_64
__visible pudval_t xen_pud_val(pud_t pud)
{
        return pte_mfn_to_pfn(pud.pud);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_pud_val);

__visible pud_t xen_make_pud(pudval_t pud)
{
        pud = pte_pfn_to_mfn(pud);

        return native_make_pud(pud);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_make_pud);

static pgd_t *xen_get_user_pgd(pgd_t *pgd)
{
        pgd_t *pgd_page = (pgd_t *)(((unsigned long)pgd) & PAGE_MASK);
        unsigned offset = pgd - pgd_page;
        pgd_t *user_ptr = NULL;

        if (offset < pgd_index(USER_LIMIT)) {
                struct page *page = virt_to_page(pgd_page);
                user_ptr = (pgd_t *)page->private;
                if (user_ptr)
                        user_ptr += offset;
        }

        return user_ptr;
}

static void __xen_set_p4d_hyper(p4d_t *ptr, p4d_t val)
{
        struct mmu_update u;

        u.ptr = virt_to_machine(ptr).maddr;
        u.val = p4d_val_ma(val);
        xen_extend_mmu_update(&u);
}

/*
 * Raw hypercall-based set_p4d, intended for in early boot before
 * there's a page structure.  This implies:
 *  1. The only existing pagetable is the kernel's
 *  2. It is always pinned
 *  3. It has no user pagetable attached to it
 */
static void __init xen_set_p4d_hyper(p4d_t *ptr, p4d_t val)
{
        preempt_disable();

        xen_mc_batch();

        __xen_set_p4d_hyper(ptr, val);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_set_p4d(p4d_t *ptr, p4d_t val)
{
        pgd_t *user_ptr = xen_get_user_pgd((pgd_t *)ptr);
        pgd_t pgd_val;

        trace_xen_mmu_set_p4d(ptr, (p4d_t *)user_ptr, val);

        /* If page is not pinned, we can just update the entry
           directly */
        if (!xen_page_pinned(ptr)) {
                *ptr = val;
                if (user_ptr) {
                        WARN_ON(xen_page_pinned(user_ptr));
                        pgd_val.pgd = p4d_val_ma(val);
                        *user_ptr = pgd_val;
                }
                return;
        }

        /* If it's pinned, then we can at least batch the kernel and
           user updates together. */
        xen_mc_batch();

        __xen_set_p4d_hyper(ptr, val);
        if (user_ptr)
                __xen_set_p4d_hyper((p4d_t *)user_ptr, val);

        xen_mc_issue(PARAVIRT_LAZY_MMU);
}
#endif  /* CONFIG_X86_64 */

static int xen_pmd_walk(struct mm_struct *mm, pmd_t *pmd,
                int (*func)(struct mm_struct *mm, struct page *, enum pt_level),
                bool last, unsigned long limit)
{
        int i, nr, flush = 0;

        nr = last ? pmd_index(limit) + 1 : PTRS_PER_PMD;
        for (i = 0; i < nr; i++) {
                if (!pmd_none(pmd[i]))
                        flush |= (*func)(mm, pmd_page(pmd[i]), PT_PTE);
        }
        return flush;
}

static int xen_pud_walk(struct mm_struct *mm, pud_t *pud,
                int (*func)(struct mm_struct *mm, struct page *, enum pt_level),
                bool last, unsigned long limit)
{
        int i, nr, flush = 0;

        nr = last ? pud_index(limit) + 1 : PTRS_PER_PUD;
        for (i = 0; i < nr; i++) {
                pmd_t *pmd;

                if (pud_none(pud[i]))
                        continue;

                pmd = pmd_offset(&pud[i], 0);
                if (PTRS_PER_PMD > 1)
                        flush |= (*func)(mm, virt_to_page(pmd), PT_PMD);
                flush |= xen_pmd_walk(mm, pmd, func,
                                last && i == nr - 1, limit);
        }
        return flush;
}

static int xen_p4d_walk(struct mm_struct *mm, p4d_t *p4d,
                int (*func)(struct mm_struct *mm, struct page *, enum pt_level),
                bool last, unsigned long limit)
{
        int flush = 0;
        pud_t *pud;


        if (p4d_none(*p4d))
                return flush;

        pud = pud_offset(p4d, 0);
        if (PTRS_PER_PUD > 1)
                flush |= (*func)(mm, virt_to_page(pud), PT_PUD);
        flush |= xen_pud_walk(mm, pud, func, last, limit);
        return flush;
}

/*
 * (Yet another) pagetable walker.  This one is intended for pinning a
 * pagetable.  This means that it walks a pagetable and calls the
 * callback function on each page it finds making up the page table,
 * at every level.  It walks the entire pagetable, but it only bothers
 * pinning pte pages which are below limit.  In the normal case this
 * will be STACK_TOP_MAX, but at boot we need to pin up to
 * FIXADDR_TOP.
 *
 * For 32-bit the important bit is that we don't pin beyond there,
 * because then we start getting into Xen's ptes.
 *
 * For 64-bit, we must skip the Xen hole in the middle of the address
 * space, just after the big x86-64 virtual hole.
 */
static int __xen_pgd_walk(struct mm_struct *mm, pgd_t *pgd,
                          int (*func)(struct mm_struct *mm, struct page *,
                                      enum pt_level),
                          unsigned long limit)
{
        int i, nr, flush = 0;
        unsigned hole_low, hole_high;

        /* The limit is the last byte to be touched */
        limit--;
        BUG_ON(limit >= FIXADDR_TOP);

        /*
         * 64-bit has a great big hole in the middle of the address
         * space, which contains the Xen mappings.  On 32-bit these
         * will end up making a zero-sized hole and so is a no-op.
         */
        hole_low = pgd_index(USER_LIMIT);
        hole_high = pgd_index(PAGE_OFFSET);

        nr = pgd_index(limit) + 1;
        for (i = 0; i < nr; i++) {
                p4d_t *p4d;

                if (i >= hole_low && i < hole_high)
                        continue;

                if (pgd_none(pgd[i]))
                        continue;

                p4d = p4d_offset(&pgd[i], 0);
                flush |= xen_p4d_walk(mm, p4d, func, i == nr - 1, limit);
        }

        /* Do the top level last, so that the callbacks can use it as
           a cue to do final things like tlb flushes. */
        flush |= (*func)(mm, virt_to_page(pgd), PT_PGD);

        return flush;
}

static int xen_pgd_walk(struct mm_struct *mm,
                        int (*func)(struct mm_struct *mm, struct page *,
                                    enum pt_level),
                        unsigned long limit)
{
        return __xen_pgd_walk(mm, mm->pgd, func, limit);
}

/* If we're using split pte locks, then take the page's lock and
   return a pointer to it.  Otherwise return NULL. */
static spinlock_t *xen_pte_lock(struct page *page, struct mm_struct *mm)
{
        spinlock_t *ptl = NULL;

#if USE_SPLIT_PTE_PTLOCKS
        ptl = ptlock_ptr(page);
        spin_lock_nest_lock(ptl, &mm->page_table_lock);
#endif

        return ptl;
}

static void xen_pte_unlock(void *v)
{
        spinlock_t *ptl = v;
        spin_unlock(ptl);
}

static void xen_do_pin(unsigned level, unsigned long pfn)
{
        struct mmuext_op op;

        op.cmd = level;
        op.arg1.mfn = pfn_to_mfn(pfn);

        xen_extend_mmuext_op(&op);
}

static int xen_pin_page(struct mm_struct *mm, struct page *page,
                        enum pt_level level)
{
        unsigned pgfl = TestSetPagePinned(page);
        int flush;

        if (pgfl)
                flush = 0;              /* already pinned */
        else if (PageHighMem(page))
                /* kmaps need flushing if we found an unpinned
                   highpage */
                flush = 1;
        else {
                void *pt = lowmem_page_address(page);
                unsigned long pfn = page_to_pfn(page);
                struct multicall_space mcs = __xen_mc_entry(0);
                spinlock_t *ptl;

                flush = 0;

                /*
                 * We need to hold the pagetable lock between the time
                 * we make the pagetable RO and when we actually pin
                 * it.  If we don't, then other users may come in and
                 * attempt to update the pagetable by writing it,
                 * which will fail because the memory is RO but not
                 * pinned, so Xen won't do the trap'n'emulate.
                 *
                 * If we're using split pte locks, we can't hold the
                 * entire pagetable's worth of locks during the
                 * traverse, because we may wrap the preempt count (8
                 * bits).  The solution is to mark RO and pin each PTE
                 * page while holding the lock.  This means the number
                 * of locks we end up holding is never more than a
                 * batch size (~32 entries, at present).
                 *
                 * If we're not using split pte locks, we needn't pin
                 * the PTE pages independently, because we're
                 * protected by the overall pagetable lock.
                 */
                ptl = NULL;
                if (level == PT_PTE)
                        ptl = xen_pte_lock(page, mm);

                MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
                                        pfn_pte(pfn, PAGE_KERNEL_RO),
                                        level == PT_PGD ? UVMF_TLB_FLUSH : 0);

                if (ptl) {
                        xen_do_pin(MMUEXT_PIN_L1_TABLE, pfn);

                        /* Queue a deferred unlock for when this batch
                           is completed. */
                        xen_mc_callback(xen_pte_unlock, ptl);
                }
        }

        return flush;
}

/* This is called just after a mm has been created, but it has not
   been used yet.  We need to make sure that its pagetable is all
   read-only, and can be pinned. */
static void __xen_pgd_pin(struct mm_struct *mm, pgd_t *pgd)
{
        trace_xen_mmu_pgd_pin(mm, pgd);

        xen_mc_batch();

        if (__xen_pgd_walk(mm, pgd, xen_pin_page, USER_LIMIT)) {
                /* re-enable interrupts for flushing */
                xen_mc_issue(0);

                kmap_flush_unused();

                xen_mc_batch();
        }

#ifdef CONFIG_X86_64
        {
                pgd_t *user_pgd = xen_get_user_pgd(pgd);

                xen_do_pin(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa(pgd)));

                if (user_pgd) {
                        xen_pin_page(mm, virt_to_page(user_pgd), PT_PGD);
                        xen_do_pin(MMUEXT_PIN_L4_TABLE,
                                   PFN_DOWN(__pa(user_pgd)));
                }
        }
#else /* CONFIG_X86_32 */
#ifdef CONFIG_X86_PAE
        /* Need to make sure unshared kernel PMD is pinnable */
        xen_pin_page(mm, pgd_page(pgd[pgd_index(TASK_SIZE)]),
                     PT_PMD);
#endif
        xen_do_pin(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(pgd)));
#endif /* CONFIG_X86_64 */
        xen_mc_issue(0);
}

static void xen_pgd_pin(struct mm_struct *mm)
{
        __xen_pgd_pin(mm, mm->pgd);
}

/*
 * On save, we need to pin all pagetables to make sure they get their
 * mfns turned into pfns.  Search the list for any unpinned pgds and pin
 * them (unpinned pgds are not currently in use, probably because the
 * process is under construction or destruction).
 *
 * Expected to be called in stop_machine() ("equivalent to taking
 * every spinlock in the system"), so the locking doesn't really
 * matter all that much.
 */
void xen_mm_pin_all(void)
{
        struct page *page;

        spin_lock(&pgd_lock);

        list_for_each_entry(page, &pgd_list, lru) {
                if (!PagePinned(page)) {
                        __xen_pgd_pin(&init_mm, (pgd_t *)page_address(page));
                        SetPageSavePinned(page);
                }
        }

        spin_unlock(&pgd_lock);
}

/*
 * The init_mm pagetable is really pinned as soon as its created, but
 * that's before we have page structures to store the bits.  So do all
 * the book-keeping now.
 */
static int __init xen_mark_pinned(struct mm_struct *mm, struct page *page,
                                  enum pt_level level)
{
        SetPagePinned(page);
        return 0;
}

static void __init xen_mark_init_mm_pinned(void)
{
        xen_pgd_walk(&init_mm, xen_mark_pinned, FIXADDR_TOP);
}

static int xen_unpin_page(struct mm_struct *mm, struct page *page,
                          enum pt_level level)
{
        unsigned pgfl = TestClearPagePinned(page);

        if (pgfl && !PageHighMem(page)) {
                void *pt = lowmem_page_address(page);
                unsigned long pfn = page_to_pfn(page);
                spinlock_t *ptl = NULL;
                struct multicall_space mcs;

                /*
                 * Do the converse to pin_page.  If we're using split
                 * pte locks, we must be holding the lock for while
                 * the pte page is unpinned but still RO to prevent
                 * concurrent updates from seeing it in this
                 * partially-pinned state.
                 */
                if (level == PT_PTE) {
                        ptl = xen_pte_lock(page, mm);

                        if (ptl)
                                xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
                }

                mcs = __xen_mc_entry(0);

                MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
                                        pfn_pte(pfn, PAGE_KERNEL),
                                        level == PT_PGD ? UVMF_TLB_FLUSH : 0);

                if (ptl) {
                        /* unlock when batch completed */
                        xen_mc_callback(xen_pte_unlock, ptl);
                }
        }

        return 0;               /* never need to flush on unpin */
}

/* Release a pagetables pages back as normal RW */
static void __xen_pgd_unpin(struct mm_struct *mm, pgd_t *pgd)
{
        trace_xen_mmu_pgd_unpin(mm, pgd);

        xen_mc_batch();

        xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));

#ifdef CONFIG_X86_64
        {
                pgd_t *user_pgd = xen_get_user_pgd(pgd);

                if (user_pgd) {
                        xen_do_pin(MMUEXT_UNPIN_TABLE,
                                   PFN_DOWN(__pa(user_pgd)));
                        xen_unpin_page(mm, virt_to_page(user_pgd), PT_PGD);
                }
        }
#endif

#ifdef CONFIG_X86_PAE
        /* Need to make sure unshared kernel PMD is unpinned */
        xen_unpin_page(mm, pgd_page(pgd[pgd_index(TASK_SIZE)]),
                       PT_PMD);
#endif

        __xen_pgd_walk(mm, pgd, xen_unpin_page, USER_LIMIT);

        xen_mc_issue(0);
}

static void xen_pgd_unpin(struct mm_struct *mm)
{
        __xen_pgd_unpin(mm, mm->pgd);
}

/*
 * On resume, undo any pinning done at save, so that the rest of the
 * kernel doesn't see any unexpected pinned pagetables.
 */
void xen_mm_unpin_all(void)
{
        struct page *page;

        spin_lock(&pgd_lock);

        list_for_each_entry(page, &pgd_list, lru) {
                if (PageSavePinned(page)) {
                        BUG_ON(!PagePinned(page));
                        __xen_pgd_unpin(&init_mm, (pgd_t *)page_address(page));
                        ClearPageSavePinned(page);
                }
        }

        spin_unlock(&pgd_lock);
}

static void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
{
        spin_lock(&next->page_table_lock);
        xen_pgd_pin(next);
        spin_unlock(&next->page_table_lock);
}

static void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
{
        spin_lock(&mm->page_table_lock);
        xen_pgd_pin(mm);
        spin_unlock(&mm->page_table_lock);
}

static void drop_mm_ref_this_cpu(void *info)
{
        struct mm_struct *mm = info;

        if (this_cpu_read(cpu_tlbstate.loaded_mm) == mm)
                leave_mm(smp_processor_id());

        /*
         * If this cpu still has a stale cr3 reference, then make sure
         * it has been flushed.
         */
        if (this_cpu_read(xen_current_cr3) == __pa(mm->pgd))
                xen_mc_flush();
}

#ifdef CONFIG_SMP
/*
 * Another cpu may still have their %cr3 pointing at the pagetable, so
 * we need to repoint it somewhere else before we can unpin it.
 */
static void xen_drop_mm_ref(struct mm_struct *mm)
{
        cpumask_var_t mask;
        unsigned cpu;

        drop_mm_ref_this_cpu(mm);

        /* Get the "official" set of cpus referring to our pagetable. */
        if (!alloc_cpumask_var(&mask, GFP_ATOMIC)) {
                for_each_online_cpu(cpu) {
                        if (per_cpu(xen_current_cr3, cpu) != __pa(mm->pgd))
                                continue;
                        smp_call_function_single(cpu, drop_mm_ref_this_cpu, mm, 1);
                }
                return;
        }

        /*
         * It's possible that a vcpu may have a stale reference to our
         * cr3, because its in lazy mode, and it hasn't yet flushed
         * its set of pending hypercalls yet.  In this case, we can
         * look at its actual current cr3 value, and force it to flush
         * if needed.
         */
        cpumask_clear(mask);
        for_each_online_cpu(cpu) {
                if (per_cpu(xen_current_cr3, cpu) == __pa(mm->pgd))
                        cpumask_set_cpu(cpu, mask);
        }

        smp_call_function_many(mask, drop_mm_ref_this_cpu, mm, 1);
        free_cpumask_var(mask);
}
#else
static void xen_drop_mm_ref(struct mm_struct *mm)
{
        drop_mm_ref_this_cpu(mm);
}
#endif

/*
 * While a process runs, Xen pins its pagetables, which means that the
 * hypervisor forces it to be read-only, and it controls all updates
 * to it.  This means that all pagetable updates have to go via the
 * hypervisor, which is moderately expensive.
 *
 * Since we're pulling the pagetable down, we switch to use init_mm,
 * unpin old process pagetable and mark it all read-write, which
 * allows further operations on it to be simple memory accesses.
 *
 * The only subtle point is that another CPU may be still using the
 * pagetable because of lazy tlb flushing.  This means we need need to
 * switch all CPUs off this pagetable before we can unpin it.
 */
static void xen_exit_mmap(struct mm_struct *mm)
{
        get_cpu();              /* make sure we don't move around */
        xen_drop_mm_ref(mm);
        put_cpu();

        spin_lock(&mm->page_table_lock);

        /* pgd may not be pinned in the error exit path of execve */
        if (xen_page_pinned(mm->pgd))
                xen_pgd_unpin(mm);

        spin_unlock(&mm->page_table_lock);
}

static void xen_post_allocator_init(void);

static void __init pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
{
        struct mmuext_op op;

        op.cmd = cmd;
        op.arg1.mfn = pfn_to_mfn(pfn);
        if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
                BUG();
}

#ifdef CONFIG_X86_64
static void __init xen_cleanhighmap(unsigned long vaddr,
                                    unsigned long vaddr_end)
{
        unsigned long kernel_end = roundup((unsigned long)_brk_end, PMD_SIZE) - 1;
        pmd_t *pmd = level2_kernel_pgt + pmd_index(vaddr);

        /* NOTE: The loop is more greedy than the cleanup_highmap variant.
         * We include the PMD passed in on _both_ boundaries. */
        for (; vaddr <= vaddr_end && (pmd < (level2_kernel_pgt + PTRS_PER_PMD));
                        pmd++, vaddr += PMD_SIZE) {
                if (pmd_none(*pmd))
                        continue;
                if (vaddr < (unsigned long) _text || vaddr > kernel_end)
                        set_pmd(pmd, __pmd(0));
        }
        /* In case we did something silly, we should crash in this function
         * instead of somewhere later and be confusing. */
        xen_mc_flush();
}

/*
 * Make a page range writeable and free it.
 */
static void __init xen_free_ro_pages(unsigned long paddr, unsigned long size)
{
        void *vaddr = __va(paddr);
        void *vaddr_end = vaddr + size;

        for (; vaddr < vaddr_end; vaddr += PAGE_SIZE)
                make_lowmem_page_readwrite(vaddr);

        memblock_free(paddr, size);
}

static void __init xen_cleanmfnmap_free_pgtbl(void *pgtbl, bool unpin)
{
        unsigned long pa = __pa(pgtbl) & PHYSICAL_PAGE_MASK;

        if (unpin)
                pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(pa));
        ClearPagePinned(virt_to_page(__va(pa)));
        xen_free_ro_pages(pa, PAGE_SIZE);
}

static void __init xen_cleanmfnmap_pmd(pmd_t *pmd, bool unpin)
{
        unsigned long pa;
        pte_t *pte_tbl;
        int i;

        if (pmd_large(*pmd)) {
                pa = pmd_val(*pmd) & PHYSICAL_PAGE_MASK;
                xen_free_ro_pages(pa, PMD_SIZE);
                return;
        }

        pte_tbl = pte_offset_kernel(pmd, 0);
        for (i = 0; i < PTRS_PER_PTE; i++) {
                if (pte_none(pte_tbl[i]))
                        continue;
                pa = pte_pfn(pte_tbl[i]) << PAGE_SHIFT;
                xen_free_ro_pages(pa, PAGE_SIZE);
        }
        set_pmd(pmd, __pmd(0));
        xen_cleanmfnmap_free_pgtbl(pte_tbl, unpin);
}

static void __init xen_cleanmfnmap_pud(pud_t *pud, bool unpin)
{
        unsigned long pa;
        pmd_t *pmd_tbl;
        int i;

        if (pud_large(*pud)) {
                pa = pud_val(*pud) & PHYSICAL_PAGE_MASK;
                xen_free_ro_pages(pa, PUD_SIZE);
                return;
        }

        pmd_tbl = pmd_offset(pud, 0);
        for (i = 0; i < PTRS_PER_PMD; i++) {
                if (pmd_none(pmd_tbl[i]))
                        continue;
                xen_cleanmfnmap_pmd(pmd_tbl + i, unpin);
        }
        set_pud(pud, __pud(0));
        xen_cleanmfnmap_free_pgtbl(pmd_tbl, unpin);
}

static void __init xen_cleanmfnmap_p4d(p4d_t *p4d, bool unpin)
{
        unsigned long pa;
        pud_t *pud_tbl;
        int i;

        if (p4d_large(*p4d)) {
                pa = p4d_val(*p4d) & PHYSICAL_PAGE_MASK;
                xen_free_ro_pages(pa, P4D_SIZE);
                return;
        }

        pud_tbl = pud_offset(p4d, 0);
        for (i = 0; i < PTRS_PER_PUD; i++) {
                if (pud_none(pud_tbl[i]))
                        continue;
                xen_cleanmfnmap_pud(pud_tbl + i, unpin);
        }
        set_p4d(p4d, __p4d(0));
        xen_cleanmfnmap_free_pgtbl(pud_tbl, unpin);
}

/*
 * Since it is well isolated we can (and since it is perhaps large we should)
 * also free the page tables mapping the initial P->M table.
 */
static void __init xen_cleanmfnmap(unsigned long vaddr)
{
        pgd_t *pgd;
        p4d_t *p4d;
        bool unpin;

        unpin = (vaddr == 2 * PGDIR_SIZE);
        vaddr &= PMD_MASK;
        pgd = pgd_offset_k(vaddr);
        p4d = p4d_offset(pgd, 0);
        if (!p4d_none(*p4d))
                xen_cleanmfnmap_p4d(p4d, unpin);
}

static void __init xen_pagetable_p2m_free(void)
{
        unsigned long size;
        unsigned long addr;

        size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));

        /* No memory or already called. */
        if ((unsigned long)xen_p2m_addr == xen_start_info->mfn_list)
                return;

        /* using __ka address and sticking INVALID_P2M_ENTRY! */
        memset((void *)xen_start_info->mfn_list, 0xff, size);

        addr = xen_start_info->mfn_list;
        /*
         * We could be in __ka space.
         * We roundup to the PMD, which means that if anybody at this stage is
         * using the __ka address of xen_start_info or
         * xen_start_info->shared_info they are in going to crash. Fortunatly
         * we have already revectored in xen_setup_kernel_pagetable and in
         * xen_setup_shared_info.
         */
        size = roundup(size, PMD_SIZE);

        if (addr >= __START_KERNEL_map) {
                xen_cleanhighmap(addr, addr + size);
                size = PAGE_ALIGN(xen_start_info->nr_pages *
                                  sizeof(unsigned long));
                memblock_free(__pa(addr), size);
        } else {
                xen_cleanmfnmap(addr);
        }
}

static void __init xen_pagetable_cleanhighmap(void)
{
        unsigned long size;
        unsigned long addr;

        /* At this stage, cleanup_highmap has already cleaned __ka space
         * from _brk_limit way up to the max_pfn_mapped (which is the end of
         * the ramdisk). We continue on, erasing PMD entries that point to page
         * tables - do note that they are accessible at this stage via __va.
         * As Xen is aligning the memory end to a 4MB boundary, for good
         * measure we also round up to PMD_SIZE * 2 - which means that if
         * anybody is using __ka address to the initial boot-stack - and try
         * to use it - they are going to crash. The xen_start_info has been
         * taken care of already in xen_setup_kernel_pagetable. */
        addr = xen_start_info->pt_base;
        size = xen_start_info->nr_pt_frames * PAGE_SIZE;

        xen_cleanhighmap(addr, roundup(addr + size, PMD_SIZE * 2));
        xen_start_info->pt_base = (unsigned long)__va(__pa(xen_start_info->pt_base));
}
#endif

static void __init xen_pagetable_p2m_setup(void)
{
        xen_vmalloc_p2m_tree();

#ifdef CONFIG_X86_64
        xen_pagetable_p2m_free();

        xen_pagetable_cleanhighmap();
#endif
        /* And revector! Bye bye old array */
        xen_start_info->mfn_list = (unsigned long)xen_p2m_addr;
}

static void __init xen_pagetable_init(void)
{
        paging_init();
        xen_post_allocator_init();

        xen_pagetable_p2m_setup();

        /* Allocate and initialize top and mid mfn levels for p2m structure */
        xen_build_mfn_list_list();

        /* Remap memory freed due to conflicts with E820 map */
        xen_remap_memory();

        xen_setup_shared_info();
}
static void xen_write_cr2(unsigned long cr2)
{
        this_cpu_read(xen_vcpu)->arch.cr2 = cr2;
}

static unsigned long xen_read_cr2(void)
{
        return this_cpu_read(xen_vcpu)->arch.cr2;
}

unsigned long xen_read_cr2_direct(void)
{
        return this_cpu_read(xen_vcpu_info.arch.cr2);
}

static void xen_flush_tlb(void)
{
        struct mmuext_op *op;
        struct multicall_space mcs;

        trace_xen_mmu_flush_tlb(0);

        preempt_disable();

        mcs = xen_mc_entry(sizeof(*op));

        op = mcs.args;
        op->cmd = MMUEXT_TLB_FLUSH_LOCAL;
        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_flush_tlb_single(unsigned long addr)
{
        struct mmuext_op *op;
        struct multicall_space mcs;

        trace_xen_mmu_flush_tlb_single(addr);

        preempt_disable();

        mcs = xen_mc_entry(sizeof(*op));
        op = mcs.args;
        op->cmd = MMUEXT_INVLPG_LOCAL;
        op->arg1.linear_addr = addr & PAGE_MASK;
        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_flush_tlb_others(const struct cpumask *cpus,
                                 const struct flush_tlb_info *info)
{
        struct {
                struct mmuext_op op;
                DECLARE_BITMAP(mask, NR_CPUS);
        } *args;
        struct multicall_space mcs;
        const size_t mc_entry_size = sizeof(args->op) +
                sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus());

        trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end);

        if (cpumask_empty(cpus))
                return;         /* nothing to do */

        mcs = xen_mc_entry(mc_entry_size);
        args = mcs.args;
        args->op.arg2.vcpumask = to_cpumask(args->mask);

        /* Remove us, and any offline CPUS. */
        cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
        cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));

        args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
        if (info->end != TLB_FLUSH_ALL &&
            (info->end - info->start) <= PAGE_SIZE) {
                args->op.cmd = MMUEXT_INVLPG_MULTI;
                args->op.arg1.linear_addr = info->start;
        }

        MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);
}

static unsigned long xen_read_cr3(void)
{
        return this_cpu_read(xen_cr3);
}

static void set_current_cr3(void *v)
{
        this_cpu_write(xen_current_cr3, (unsigned long)v);
}

static void __xen_write_cr3(bool kernel, unsigned long cr3)
{
        struct mmuext_op op;
        unsigned long mfn;

        trace_xen_mmu_write_cr3(kernel, cr3);

        if (cr3)
                mfn = pfn_to_mfn(PFN_DOWN(cr3));
        else
                mfn = 0;

        WARN_ON(mfn == 0 && kernel);

        op.cmd = kernel ? MMUEXT_NEW_BASEPTR : MMUEXT_NEW_USER_BASEPTR;
        op.arg1.mfn = mfn;

        xen_extend_mmuext_op(&op);

        if (kernel) {
                this_cpu_write(xen_cr3, cr3);

                /* Update xen_current_cr3 once the batch has actually
                   been submitted. */
                xen_mc_callback(set_current_cr3, (void *)cr3);
        }
}
static void xen_write_cr3(unsigned long cr3)
{
        BUG_ON(preemptible());

        xen_mc_batch();  /* disables interrupts */

        /* Update while interrupts are disabled, so its atomic with
           respect to ipis */
        this_cpu_write(xen_cr3, cr3);

        __xen_write_cr3(true, cr3);

#ifdef CONFIG_X86_64
        {
                pgd_t *user_pgd = xen_get_user_pgd(__va(cr3));
                if (user_pgd)
                        __xen_write_cr3(false, __pa(user_pgd));
                else
                        __xen_write_cr3(false, 0);
        }
#endif

        xen_mc_issue(PARAVIRT_LAZY_CPU);  /* interrupts restored */
}

#ifdef CONFIG_X86_64
/*
 * At the start of the day - when Xen launches a guest, it has already
 * built pagetables for the guest. We diligently look over them
 * in xen_setup_kernel_pagetable and graft as appropriate them in the
 * init_top_pgt and its friends. Then when we are happy we load
 * the new init_top_pgt - and continue on.
 *
 * The generic code starts (start_kernel) and 'init_mem_mapping' sets
 * up the rest of the pagetables. When it has completed it loads the cr3.
 * N.B. that baremetal would start at 'start_kernel' (and the early
 * #PF handler would create bootstrap pagetables) - so we are running
 * with the same assumptions as what to do when write_cr3 is executed
 * at this point.
 *
 * Since there are no user-page tables at all, we have two variants
 * of xen_write_cr3 - the early bootup (this one), and the late one
 * (xen_write_cr3). The reason we have to do that is that in 64-bit
 * the Linux kernel and user-space are both in ring 3 while the
 * hypervisor is in ring 0.
 */
static void __init xen_write_cr3_init(unsigned long cr3)
{
        BUG_ON(preemptible());

        xen_mc_batch();  /* disables interrupts */

        /* Update while interrupts are disabled, so its atomic with
           respect to ipis */
        this_cpu_write(xen_cr3, cr3);

        __xen_write_cr3(true, cr3);

        xen_mc_issue(PARAVIRT_LAZY_CPU);  /* interrupts restored */
}
#endif

static int xen_pgd_alloc(struct mm_struct *mm)
{
        pgd_t *pgd = mm->pgd;
        int ret = 0;

        BUG_ON(PagePinned(virt_to_page(pgd)));

#ifdef CONFIG_X86_64
        {
                struct page *page = virt_to_page(pgd);
                pgd_t *user_pgd;

                BUG_ON(page->private != 0);

                ret = -ENOMEM;

                user_pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
                page->private = (unsigned long)user_pgd;

                if (user_pgd != NULL) {
#ifdef CONFIG_X86_VSYSCALL_EMULATION
                        user_pgd[pgd_index(VSYSCALL_ADDR)] =
                                __pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
#endif
                        ret = 0;
                }

                BUG_ON(PagePinned(virt_to_page(xen_get_user_pgd(pgd))));
        }
#endif
        return ret;
}

static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
{
#ifdef CONFIG_X86_64
        pgd_t *user_pgd = xen_get_user_pgd(pgd);

        if (user_pgd)
                free_page((unsigned long)user_pgd);
#endif
}

/*
 * Init-time set_pte while constructing initial pagetables, which
 * doesn't allow RO page table pages to be remapped RW.
 *
 * If there is no MFN for this PFN then this page is initially
 * ballooned out so clear the PTE (as in decrease_reservation() in
 * drivers/xen/balloon.c).
 *
 * Many of these PTE updates are done on unpinned and writable pages
 * and doing a hypercall for these is unnecessary and expensive.  At
 * this point it is not possible to tell if a page is pinned or not,
 * so always write the PTE directly and rely on Xen trapping and
 * emulating any updates as necessary.
 */
__visible pte_t xen_make_pte_init(pteval_t pte)
{
#ifdef CONFIG_X86_64
        unsigned long pfn;

        /*
         * Pages belonging to the initial p2m list mapped outside the default
         * address range must be mapped read-only. This region contains the
         * page tables for mapping the p2m list, too, and page tables MUST be
         * mapped read-only.
         */
        pfn = (pte & PTE_PFN_MASK) >> PAGE_SHIFT;
        if (xen_start_info->mfn_list < __START_KERNEL_map &&
            pfn >= xen_start_info->first_p2m_pfn &&
            pfn < xen_start_info->first_p2m_pfn + xen_start_info->nr_p2m_frames)
                pte &= ~_PAGE_RW;
#endif
        pte = pte_pfn_to_mfn(pte);
        return native_make_pte(pte);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte_init);

static void __init xen_set_pte_init(pte_t *ptep, pte_t pte)
{
#ifdef CONFIG_X86_32
        /* If there's an existing pte, then don't allow _PAGE_RW to be set */
        if (pte_mfn(pte) != INVALID_P2M_ENTRY
            && pte_val_ma(*ptep) & _PAGE_PRESENT)
                pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
                               pte_val_ma(pte));
#endif
        native_set_pte(ptep, pte);
}

/* Early in boot, while setting up the initial pagetable, assume
   everything is pinned. */
static void __init xen_alloc_pte_init(struct mm_struct *mm, unsigned long pfn)
{
#ifdef CONFIG_FLATMEM
        BUG_ON(mem_map);        /* should only be used early */
#endif
        make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
        pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
}

/* Used for pmd and pud */
static void __init xen_alloc_pmd_init(struct mm_struct *mm, unsigned long pfn)
{
#ifdef CONFIG_FLATMEM
        BUG_ON(mem_map);        /* should only be used early */
#endif
        make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
}

/* Early release_pte assumes that all pts are pinned, since there's
   only init_mm and anything attached to that is pinned. */
static void __init xen_release_pte_init(unsigned long pfn)
{
        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
        make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
}

static void __init xen_release_pmd_init(unsigned long pfn)
{
        make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
}

static inline void __pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
{
        struct multicall_space mcs;
        struct mmuext_op *op;

        mcs = __xen_mc_entry(sizeof(*op));
        op = mcs.args;
        op->cmd = cmd;
        op->arg1.mfn = pfn_to_mfn(pfn);

        MULTI_mmuext_op(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
}

static inline void __set_pfn_prot(unsigned long pfn, pgprot_t prot)
{
        struct multicall_space mcs;
        unsigned long addr = (unsigned long)__va(pfn << PAGE_SHIFT);

        mcs = __xen_mc_entry(0);
        MULTI_update_va_mapping(mcs.mc, (unsigned long)addr,
                                pfn_pte(pfn, prot), 0);
}

/* This needs to make sure the new pte page is pinned iff its being
   attached to a pinned pagetable. */
static inline void xen_alloc_ptpage(struct mm_struct *mm, unsigned long pfn,
                                    unsigned level)
{
        bool pinned = PagePinned(virt_to_page(mm->pgd));

        trace_xen_mmu_alloc_ptpage(mm, pfn, level, pinned);

        if (pinned) {
                struct page *page = pfn_to_page(pfn);

                SetPagePinned(page);

                if (!PageHighMem(page)) {
                        xen_mc_batch();

                        __set_pfn_prot(pfn, PAGE_KERNEL_RO);

                        if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS)
                                __pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);

                        xen_mc_issue(PARAVIRT_LAZY_MMU);
                } else {
                        /* make sure there are no stray mappings of
                           this page */
                        kmap_flush_unused();
                }
        }
}

static void xen_alloc_pte(struct mm_struct *mm, unsigned long pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PTE);
}

static void xen_alloc_pmd(struct mm_struct *mm, unsigned long pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PMD);
}

/* This should never happen until we're OK to use struct page */
static inline void xen_release_ptpage(unsigned long pfn, unsigned level)
{
        struct page *page = pfn_to_page(pfn);
        bool pinned = PagePinned(page);

        trace_xen_mmu_release_ptpage(pfn, level, pinned);

        if (pinned) {
                if (!PageHighMem(page)) {
                        xen_mc_batch();

                        if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS)
                                __pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);

                        __set_pfn_prot(pfn, PAGE_KERNEL);

                        xen_mc_issue(PARAVIRT_LAZY_MMU);
                }
                ClearPagePinned(page);
        }
}

static void xen_release_pte(unsigned long pfn)
{
        xen_release_ptpage(pfn, PT_PTE);
}

static void xen_release_pmd(unsigned long pfn)
{
        xen_release_ptpage(pfn, PT_PMD);
}

#ifdef CONFIG_X86_64
static void xen_alloc_pud(struct mm_struct *mm, unsigned long pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PUD);
}

static void xen_release_pud(unsigned long pfn)
{
        xen_release_ptpage(pfn, PT_PUD);
}
#endif

void __init xen_reserve_top(void)
{
#ifdef CONFIG_X86_32
        unsigned long top = HYPERVISOR_VIRT_START;
        struct xen_platform_parameters pp;

        if (HYPERVISOR_xen_version(XENVER_platform_parameters, &pp) == 0)
                top = pp.virt_start;

        reserve_top_address(-top);
#endif  /* CONFIG_X86_32 */
}

/*
 * Like __va(), but returns address in the kernel mapping (which is
 * all we have until the physical memory mapping has been set up.
 */
static void * __init __ka(phys_addr_t paddr)
{
#ifdef CONFIG_X86_64
        return (void *)(paddr + __START_KERNEL_map);
#else
        return __va(paddr);
#endif
}

/* Convert a machine address to physical address */
static unsigned long __init m2p(phys_addr_t maddr)
{
        phys_addr_t paddr;

        maddr &= XEN_PTE_MFN_MASK;
        paddr = mfn_to_pfn(maddr >> PAGE_SHIFT) << PAGE_SHIFT;

        return paddr;
}

/* Convert a machine address to kernel virtual */
static void * __init m2v(phys_addr_t maddr)
{
        return __ka(m2p(maddr));
}

/* Set the page permissions on an identity-mapped pages */
static void __init set_page_prot_flags(void *addr, pgprot_t prot,
                                       unsigned long flags)
{
        unsigned long pfn = __pa(addr) >> PAGE_SHIFT;
        pte_t pte = pfn_pte(pfn, prot);

        if (HYPERVISOR_update_va_mapping((unsigned long)addr, pte, flags))
                BUG();
}
static void __init set_page_prot(void *addr, pgprot_t prot)
{
        return set_page_prot_flags(addr, prot, UVMF_NONE);
}
#ifdef CONFIG_X86_32
static void __init xen_map_identity_early(pmd_t *pmd, unsigned long max_pfn)
{
        unsigned pmdidx, pteidx;
        unsigned ident_pte;
        unsigned long pfn;

        level1_ident_pgt = extend_brk(sizeof(pte_t) * LEVEL1_IDENT_ENTRIES,
                                      PAGE_SIZE);

        ident_pte = 0;
        pfn = 0;
        for (pmdidx = 0; pmdidx < PTRS_PER_PMD && pfn < max_pfn; pmdidx++) {
                pte_t *pte_page;

                /* Reuse or allocate a page of ptes */
                if (pmd_present(pmd[pmdidx]))
                        pte_page = m2v(pmd[pmdidx].pmd);
                else {
                        /* Check for free pte pages */
                        if (ident_pte == LEVEL1_IDENT_ENTRIES)
                                break;

                        pte_page = &level1_ident_pgt[ident_pte];
                        ident_pte += PTRS_PER_PTE;

                        pmd[pmdidx] = __pmd(__pa(pte_page) | _PAGE_TABLE);
                }

                /* Install mappings */
                for (pteidx = 0; pteidx < PTRS_PER_PTE; pteidx++, pfn++) {
                        pte_t pte;

                        if (pfn > max_pfn_mapped)
                                max_pfn_mapped = pfn;

                        if (!pte_none(pte_page[pteidx]))
                                continue;

                        pte = pfn_pte(pfn, PAGE_KERNEL_EXEC);
                        pte_page[pteidx] = pte;
                }
        }

        for (pteidx = 0; pteidx < ident_pte; pteidx += PTRS_PER_PTE)
                set_page_prot(&level1_ident_pgt[pteidx], PAGE_KERNEL_RO);

        set_page_prot(pmd, PAGE_KERNEL_RO);
}
#endif
void __init xen_setup_machphys_mapping(void)
{
        struct xen_machphys_mapping mapping;

        if (HYPERVISOR_memory_op(XENMEM_machphys_mapping, &mapping) == 0) {
                machine_to_phys_mapping = (unsigned long *)mapping.v_start;
                machine_to_phys_nr = mapping.max_mfn + 1;
        } else {
                machine_to_phys_nr = MACH2PHYS_NR_ENTRIES;
        }
#ifdef CONFIG_X86_32
        WARN_ON((machine_to_phys_mapping + (machine_to_phys_nr - 1))
                < machine_to_phys_mapping);
#endif
}

#ifdef CONFIG_X86_64
static void __init convert_pfn_mfn(void *v)
{
        pte_t *pte = v;
        int i;

        /* All levels are converted the same way, so just treat them
           as ptes. */
        for (i = 0; i < PTRS_PER_PTE; i++)
                pte[i] = xen_make_pte(pte[i].pte);
}
static void __init check_pt_base(unsigned long *pt_base, unsigned long *pt_end,
                                 unsigned long addr)
{
        if (*pt_base == PFN_DOWN(__pa(addr))) {
                set_page_prot_flags((void *)addr, PAGE_KERNEL, UVMF_INVLPG);
                clear_page((void *)addr);
                (*pt_base)++;
        }
        if (*pt_end == PFN_DOWN(__pa(addr))) {
                set_page_prot_flags((void *)addr, PAGE_KERNEL, UVMF_INVLPG);
                clear_page((void *)addr);
                (*pt_end)--;
        }
}
/*
 * Set up the initial kernel pagetable.
 *
 * We can construct this by grafting the Xen provided pagetable into
 * head_64.S's preconstructed pagetables.  We copy the Xen L2's into
 * level2_ident_pgt, and level2_kernel_pgt.  This means that only the
 * kernel has a physical mapping to start with - but that's enough to
 * get __va working.  We need to fill in the rest of the physical
 * mapping once some sort of allocator has been set up.
 */
void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
{
        pud_t *l3;
        pmd_t *l2;
        unsigned long addr[3];
        unsigned long pt_base, pt_end;
        unsigned i;

        /* max_pfn_mapped is the last pfn mapped in the initial memory
         * mappings. Considering that on Xen after the kernel mappings we
         * have the mappings of some pages that don't exist in pfn space, we
         * set max_pfn_mapped to the last real pfn mapped. */
        if (xen_start_info->mfn_list < __START_KERNEL_map)
                max_pfn_mapped = xen_start_info->first_p2m_pfn;
        else
                max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->mfn_list));

        pt_base = PFN_DOWN(__pa(xen_start_info->pt_base));
        pt_end = pt_base + xen_start_info->nr_pt_frames;

        /* Zap identity mapping */
        init_top_pgt[0] = __pgd(0);

        /* Pre-constructed entries are in pfn, so convert to mfn */
        /* L4[272] -> level3_ident_pgt  */
        /* L4[511] -> level3_kernel_pgt */
        convert_pfn_mfn(init_top_pgt);

        /* L3_i[0] -> level2_ident_pgt */
        convert_pfn_mfn(level3_ident_pgt);
        /* L3_k[510] -> level2_kernel_pgt */
        /* L3_k[511] -> level2_fixmap_pgt */
        convert_pfn_mfn(level3_kernel_pgt);

        /* L3_k[511][506] -> level1_fixmap_pgt */
        convert_pfn_mfn(level2_fixmap_pgt);

        /* We get [511][511] and have Xen's version of level2_kernel_pgt */
        l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd);
        l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud);

        addr[0] = (unsigned long)pgd;
        addr[1] = (unsigned long)l3;
        addr[2] = (unsigned long)l2;
        /* Graft it onto L4[272][0]. Note that we creating an aliasing problem:
         * Both L4[272][0] and L4[511][510] have entries that point to the same
         * L2 (PMD) tables. Meaning that if you modify it in __va space
         * it will be also modified in the __ka space! (But if you just
         * modify the PMD table to point to other PTE's or none, then you
         * are OK - which is what cleanup_highmap does) */
        copy_page(level2_ident_pgt, l2);
        /* Graft it onto L4[511][510] */
        copy_page(level2_kernel_pgt, l2);

        /*
         * Zap execute permission from the ident map. Due to the sharing of
         * L1 entries we need to do this in the L2.
         */
        if (__supported_pte_mask & _PAGE_NX) {
                for (i = 0; i < PTRS_PER_PMD; ++i) {
                        if (pmd_none(level2_ident_pgt[i]))
                                continue;
                        level2_ident_pgt[i] = pmd_set_flags(level2_ident_pgt[i], _PAGE_NX);
                }
        }

        /* Copy the initial P->M table mappings if necessary. */
        i = pgd_index(xen_start_info->mfn_list);
        if (i && i < pgd_index(__START_KERNEL_map))
                init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];

        /* Make pagetable pieces RO */
        set_page_prot(init_top_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_kernel_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_user_vsyscall, PAGE_KERNEL_RO);
        set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
        set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
        set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
        set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO);

        /* Pin down new L4 */
        pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,
                          PFN_DOWN(__pa_symbol(init_top_pgt)));

        /* Unpin Xen-provided one */
        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));

        /*
         * At this stage there can be no user pgd, and no page structure to
         * attach it to, so make sure we just set kernel pgd.
         */
        xen_mc_batch();
        __xen_write_cr3(true, __pa(init_top_pgt));
        xen_mc_issue(PARAVIRT_LAZY_CPU);

        /* We can't that easily rip out L3 and L2, as the Xen pagetables are
         * set out this way: [L4], [L1], [L2], [L3], [L1], [L1] ...  for
         * the initial domain. For guests using the toolstack, they are in:
         * [L4], [L3], [L2], [L1], [L1], order .. So for dom0 we can only
         * rip out the [L4] (pgd), but for guests we shave off three pages.
         */
        for (i = 0; i < ARRAY_SIZE(addr); i++)
                check_pt_base(&pt_base, &pt_end, addr[i]);

        /* Our (by three pages) smaller Xen pagetable that we are using */
        xen_pt_base = PFN_PHYS(pt_base);
        xen_pt_size = (pt_end - pt_base) * PAGE_SIZE;
        memblock_reserve(xen_pt_base, xen_pt_size);

        /* Revector the xen_start_info */
        xen_start_info = (struct start_info *)__va(__pa(xen_start_info));
}

/*
 * Read a value from a physical address.
 */
static unsigned long __init xen_read_phys_ulong(phys_addr_t addr)
{
        unsigned long *vaddr;
        unsigned long val;

        vaddr = early_memremap_ro(addr, sizeof(val));
        val = *vaddr;
        early_memunmap(vaddr, sizeof(val));
        return val;
}

/*
 * Translate a virtual address to a physical one without relying on mapped
 * page tables. Don't rely on big pages being aligned in (guest) physical
 * space!
 */
static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
{
        phys_addr_t pa;
        pgd_t pgd;
        pud_t pud;
        pmd_t pmd;
        pte_t pte;

        pa = read_cr3_pa();
        pgd = native_make_pgd(xen_read_phys_ulong(pa + pgd_index(vaddr) *
                                                       sizeof(pgd)));
        if (!pgd_present(pgd))
                return 0;

        pa = pgd_val(pgd) & PTE_PFN_MASK;
        pud = native_make_pud(xen_read_phys_ulong(pa + pud_index(vaddr) *
                                                       sizeof(pud)));
        if (!pud_present(pud))
                return 0;
        pa = pud_val(pud) & PTE_PFN_MASK;
        if (pud_large(pud))
                return pa + (vaddr & ~PUD_MASK);

        pmd = native_make_pmd(xen_read_phys_ulong(pa + pmd_index(vaddr) *
                                                       sizeof(pmd)));
        if (!pmd_present(pmd))
                return 0;
        pa = pmd_val(pmd) & PTE_PFN_MASK;
        if (pmd_large(pmd))
                return pa + (vaddr & ~PMD_MASK);

        pte = native_make_pte(xen_read_phys_ulong(pa + pte_index(vaddr) *
                                                       sizeof(pte)));
        if (!pte_present(pte))
                return 0;
        pa = pte_pfn(pte) << PAGE_SHIFT;

        return pa | (vaddr & ~PAGE_MASK);
}

/*
 * Find a new area for the hypervisor supplied p2m list and relocate the p2m to
 * this area.
 */
void __init xen_relocate_p2m(void)
{
        phys_addr_t size, new_area, pt_phys, pmd_phys, pud_phys;
        unsigned long p2m_pfn, p2m_pfn_end, n_frames, pfn, pfn_end;
        int n_pte, n_pt, n_pmd, n_pud, idx_pte, idx_pt, idx_pmd, idx_pud;
        pte_t *pt;
        pmd_t *pmd;
        pud_t *pud;
        pgd_t *pgd;
        unsigned long *new_p2m;
        int save_pud;

        size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
        n_pte = roundup(size, PAGE_SIZE) >> PAGE_SHIFT;
        n_pt = roundup(size, PMD_SIZE) >> PMD_SHIFT;
        n_pmd = roundup(size, PUD_SIZE) >> PUD_SHIFT;
        n_pud = roundup(size, P4D_SIZE) >> P4D_SHIFT;
        n_frames = n_pte + n_pt + n_pmd + n_pud;

        new_area = xen_find_free_area(PFN_PHYS(n_frames));
        if (!new_area) {
                xen_raw_console_write("Can't find new memory area for p2m needed due to E820 map conflict\n");
                BUG();
        }

        /*
         * Setup the page tables for addressing the new p2m list.
         * We have asked the hypervisor to map the p2m list at the user address
         * PUD_SIZE. It may have done so, or it may have used a kernel space
         * address depending on the Xen version.
         * To avoid any possible virtual address collision, just use
         * 2 * PUD_SIZE for the new area.
         */
        pud_phys = new_area;
        pmd_phys = pud_phys + PFN_PHYS(n_pud);
        pt_phys = pmd_phys + PFN_PHYS(n_pmd);
        p2m_pfn = PFN_DOWN(pt_phys) + n_pt;

        pgd = __va(read_cr3_pa());
        new_p2m = (unsigned long *)(2 * PGDIR_SIZE);
        save_pud = n_pud;
        for (idx_pud = 0; idx_pud < n_pud; idx_pud++) {
                pud = early_memremap(pud_phys, PAGE_SIZE);
                clear_page(pud);
                for (idx_pmd = 0; idx_pmd < min(n_pmd, PTRS_PER_PUD);
                                idx_pmd++) {
                        pmd = early_memremap(pmd_phys, PAGE_SIZE);
                        clear_page(pmd);
                        for (idx_pt = 0; idx_pt < min(n_pt, PTRS_PER_PMD);
                                        idx_pt++) {
                                pt = early_memremap(pt_phys, PAGE_SIZE);
                                clear_page(pt);
                                for (idx_pte = 0;
                                                idx_pte < min(n_pte, PTRS_PER_PTE);
                                                idx_pte++) {
                                        set_pte(pt + idx_pte,
                                                        pfn_pte(p2m_pfn, PAGE_KERNEL));
                                        p2m_pfn++;
                                }
                                n_pte -= PTRS_PER_PTE;
                                early_memunmap(pt, PAGE_SIZE);
                                make_lowmem_page_readonly(__va(pt_phys));
                                pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE,
                                                PFN_DOWN(pt_phys));
                                set_pmd(pmd + idx_pt,
                                                __pmd(_PAGE_TABLE | pt_phys));
                                pt_phys += PAGE_SIZE;
                        }
                        n_pt -= PTRS_PER_PMD;
                        early_memunmap(pmd, PAGE_SIZE);
                        make_lowmem_page_readonly(__va(pmd_phys));
                        pin_pagetable_pfn(MMUEXT_PIN_L2_TABLE,
                                        PFN_DOWN(pmd_phys));
                        set_pud(pud + idx_pmd, __pud(_PAGE_TABLE | pmd_phys));
                        pmd_phys += PAGE_SIZE;
                }
                n_pmd -= PTRS_PER_PUD;
                early_memunmap(pud, PAGE_SIZE);
                make_lowmem_page_readonly(__va(pud_phys));
                pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, PFN_DOWN(pud_phys));
                set_pgd(pgd + 2 + idx_pud, __pgd(_PAGE_TABLE | pud_phys));
                pud_phys += PAGE_SIZE;
        }

        /* Now copy the old p2m info to the new area. */
        memcpy(new_p2m, xen_p2m_addr, size);
        xen_p2m_addr = new_p2m;

        /* Release the old p2m list and set new list info. */
        p2m_pfn = PFN_DOWN(xen_early_virt_to_phys(xen_start_info->mfn_list));
        BUG_ON(!p2m_pfn);
        p2m_pfn_end = p2m_pfn + PFN_DOWN(size);

        if (xen_start_info->mfn_list < __START_KERNEL_map) {
                pfn = xen_start_info->first_p2m_pfn;
                pfn_end = xen_start_info->first_p2m_pfn +
                          xen_start_info->nr_p2m_frames;
                set_pgd(pgd + 1, __pgd(0));
        } else {
                pfn = p2m_pfn;
                pfn_end = p2m_pfn_end;
        }

        memblock_free(PFN_PHYS(pfn), PAGE_SIZE * (pfn_end - pfn));
        while (pfn < pfn_end) {
                if (pfn == p2m_pfn) {
                        pfn = p2m_pfn_end;
                        continue;
                }
                make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
                pfn++;
        }

        xen_start_info->mfn_list = (unsigned long)xen_p2m_addr;
        xen_start_info->first_p2m_pfn =  PFN_DOWN(new_area);
        xen_start_info->nr_p2m_frames = n_frames;
}

#else   /* !CONFIG_X86_64 */
static RESERVE_BRK_ARRAY(pmd_t, initial_kernel_pmd, PTRS_PER_PMD);
static RESERVE_BRK_ARRAY(pmd_t, swapper_kernel_pmd, PTRS_PER_PMD);

static void __init xen_write_cr3_init(unsigned long cr3)
{
        unsigned long pfn = PFN_DOWN(__pa(swapper_pg_dir));

        BUG_ON(read_cr3_pa() != __pa(initial_page_table));
        BUG_ON(cr3 != __pa(swapper_pg_dir));

        /*
         * We are switching to swapper_pg_dir for the first time (from
         * initial_page_table) and therefore need to mark that page
         * read-only and then pin it.
         *
         * Xen disallows sharing of kernel PMDs for PAE
         * guests. Therefore we must copy the kernel PMD from
         * initial_page_table into a new kernel PMD to be used in
         * swapper_pg_dir.
         */
        swapper_kernel_pmd =
                extend_brk(sizeof(pmd_t) * PTRS_PER_PMD, PAGE_SIZE);
        copy_page(swapper_kernel_pmd, initial_kernel_pmd);
        swapper_pg_dir[KERNEL_PGD_BOUNDARY] =
                __pgd(__pa(swapper_kernel_pmd) | _PAGE_PRESENT);
        set_page_prot(swapper_kernel_pmd, PAGE_KERNEL_RO);

        set_page_prot(swapper_pg_dir, PAGE_KERNEL_RO);
        xen_write_cr3(cr3);
        pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, pfn);

        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE,
                          PFN_DOWN(__pa(initial_page_table)));
        set_page_prot(initial_page_table, PAGE_KERNEL);
        set_page_prot(initial_kernel_pmd, PAGE_KERNEL);

        pv_mmu_ops.write_cr3 = &xen_write_cr3;
}

/*
 * For 32 bit domains xen_start_info->pt_base is the pgd address which might be
 * not the first page table in the page table pool.
 * Iterate through the initial page tables to find the real page table base.
 */
static phys_addr_t __init xen_find_pt_base(pmd_t *pmd)
{
        phys_addr_t pt_base, paddr;
        unsigned pmdidx;

        pt_base = min(__pa(xen_start_info->pt_base), __pa(pmd));

        for (pmdidx = 0; pmdidx < PTRS_PER_PMD; pmdidx++)
                if (pmd_present(pmd[pmdidx]) && !pmd_large(pmd[pmdidx])) {
                        paddr = m2p(pmd[pmdidx].pmd);
                        pt_base = min(pt_base, paddr);
                }

        return pt_base;
}

void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
{
        pmd_t *kernel_pmd;

        kernel_pmd = m2v(pgd[KERNEL_PGD_BOUNDARY].pgd);

        xen_pt_base = xen_find_pt_base(kernel_pmd);
        xen_pt_size = xen_start_info->nr_pt_frames * PAGE_SIZE;

        initial_kernel_pmd =
                extend_brk(sizeof(pmd_t) * PTRS_PER_PMD, PAGE_SIZE);

        max_pfn_mapped = PFN_DOWN(xen_pt_base + xen_pt_size + 512 * 1024);

        copy_page(initial_kernel_pmd, kernel_pmd);

        xen_map_identity_early(initial_kernel_pmd, max_pfn);

        copy_page(initial_page_table, pgd);
        initial_page_table[KERNEL_PGD_BOUNDARY] =
                __pgd(__pa(initial_kernel_pmd) | _PAGE_PRESENT);

        set_page_prot(initial_kernel_pmd, PAGE_KERNEL_RO);
        set_page_prot(initial_page_table, PAGE_KERNEL_RO);
        set_page_prot(empty_zero_page, PAGE_KERNEL_RO);

        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));

        pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE,
                          PFN_DOWN(__pa(initial_page_table)));
        xen_write_cr3(__pa(initial_page_table));

        memblock_reserve(xen_pt_base, xen_pt_size);
}
#endif  /* CONFIG_X86_64 */

void __init xen_reserve_special_pages(void)
{
        phys_addr_t paddr;

        memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
        if (xen_start_info->store_mfn) {
                paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->store_mfn));
                memblock_reserve(paddr, PAGE_SIZE);
        }
        if (!xen_initial_domain()) {
                paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->console.domU.mfn));
                memblock_reserve(paddr, PAGE_SIZE);
        }
}

void __init xen_pt_check_e820(void)
{
        if (xen_is_e820_reserved(xen_pt_base, xen_pt_size)) {
                xen_raw_console_write("Xen hypervisor allocated page table memory conflicts with E820 map\n");
                BUG();
        }
}

static unsigned char dummy_mapping[PAGE_SIZE] __page_aligned_bss;

static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
{
        pte_t pte;

        phys >>= PAGE_SHIFT;

        switch (idx) {
        case FIX_BTMAP_END ... FIX_BTMAP_BEGIN:
#ifdef CONFIG_X86_32
        case FIX_WP_TEST:
# ifdef CONFIG_HIGHMEM
        case FIX_KMAP_BEGIN ... FIX_KMAP_END:
# endif
#elif defined(CONFIG_X86_VSYSCALL_EMULATION)
        case VSYSCALL_PAGE:
#endif
        case FIX_TEXT_POKE0:
        case FIX_TEXT_POKE1:
                /* All local page mappings */
                pte = pfn_pte(phys, prot);
                break;

#ifdef CONFIG_X86_LOCAL_APIC
        case FIX_APIC_BASE:     /* maps dummy local APIC */
                pte = pfn_pte(PFN_DOWN(__pa(dummy_mapping)), PAGE_KERNEL);
                break;
#endif

#ifdef CONFIG_X86_IO_APIC
        case FIX_IO_APIC_BASE_0 ... FIX_IO_APIC_BASE_END:
                /*
                 * We just don't map the IO APIC - all access is via
                 * hypercalls.  Keep the address in the pte for reference.
                 */
                pte = pfn_pte(PFN_DOWN(__pa(dummy_mapping)), PAGE_KERNEL);
                break;
#endif

        case FIX_PARAVIRT_BOOTMAP:
                /* This is an MFN, but it isn't an IO mapping from the
                   IO domain */
                pte = mfn_pte(phys, prot);
                break;

        default:
                /* By default, set_fixmap is used for hardware mappings */
                pte = mfn_pte(phys, prot);
                break;
        }

        __native_set_fixmap(idx, pte);

#ifdef CONFIG_X86_VSYSCALL_EMULATION
        /* Replicate changes to map the vsyscall page into the user
           pagetable vsyscall mapping. */
        if (idx == VSYSCALL_PAGE) {
                unsigned long vaddr = __fix_to_virt(idx);
                set_pte_vaddr_pud(level3_user_vsyscall, vaddr, pte);
        }
#endif
}

static void __init xen_post_allocator_init(void)
{
        pv_mmu_ops.set_pte = xen_set_pte;
        pv_mmu_ops.set_pmd = xen_set_pmd;
        pv_mmu_ops.set_pud = xen_set_pud;
#ifdef CONFIG_X86_64
        pv_mmu_ops.set_p4d = xen_set_p4d;
#endif

        /* This will work as long as patching hasn't happened yet
           (which it hasn't) */
        pv_mmu_ops.alloc_pte = xen_alloc_pte;
        pv_mmu_ops.alloc_pmd = xen_alloc_pmd;
        pv_mmu_ops.release_pte = xen_release_pte;
        pv_mmu_ops.release_pmd = xen_release_pmd;
#ifdef CONFIG_X86_64
        pv_mmu_ops.alloc_pud = xen_alloc_pud;
        pv_mmu_ops.release_pud = xen_release_pud;
#endif
        pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte);

#ifdef CONFIG_X86_64
        pv_mmu_ops.write_cr3 = &xen_write_cr3;
        SetPagePinned(virt_to_page(level3_user_vsyscall));
#endif
        xen_mark_init_mm_pinned();
}

static void xen_leave_lazy_mmu(void)
{
        preempt_disable();
        xen_mc_flush();
        paravirt_leave_lazy_mmu();
        preempt_enable();
}

static const struct pv_mmu_ops xen_mmu_ops __initconst = {
        .read_cr2 = xen_read_cr2,
        .write_cr2 = xen_write_cr2,

        .read_cr3 = xen_read_cr3,
        .write_cr3 = xen_write_cr3_init,

        .flush_tlb_user = xen_flush_tlb,
        .flush_tlb_kernel = xen_flush_tlb,
        .flush_tlb_single = xen_flush_tlb_single,
        .flush_tlb_others = xen_flush_tlb_others,

        .pgd_alloc = xen_pgd_alloc,
        .pgd_free = xen_pgd_free,

        .alloc_pte = xen_alloc_pte_init,
        .release_pte = xen_release_pte_init,
        .alloc_pmd = xen_alloc_pmd_init,
        .release_pmd = xen_release_pmd_init,

        .set_pte = xen_set_pte_init,
        .set_pte_at = xen_set_pte_at,
        .set_pmd = xen_set_pmd_hyper,

        .ptep_modify_prot_start = __ptep_modify_prot_start,
        .ptep_modify_prot_commit = __ptep_modify_prot_commit,

        .pte_val = PV_CALLEE_SAVE(xen_pte_val),
        .pgd_val = PV_CALLEE_SAVE(xen_pgd_val),

        .make_pte = PV_CALLEE_SAVE(xen_make_pte_init),
        .make_pgd = PV_CALLEE_SAVE(xen_make_pgd),

#ifdef CONFIG_X86_PAE
        .set_pte_atomic = xen_set_pte_atomic,
        .pte_clear = xen_pte_clear,
        .pmd_clear = xen_pmd_clear,
#endif  /* CONFIG_X86_PAE */
        .set_pud = xen_set_pud_hyper,

        .make_pmd = PV_CALLEE_SAVE(xen_make_pmd),
        .pmd_val = PV_CALLEE_SAVE(xen_pmd_val),

#ifdef CONFIG_X86_64
        .pud_val = PV_CALLEE_SAVE(xen_pud_val),
        .make_pud = PV_CALLEE_SAVE(xen_make_pud),
        .set_p4d = xen_set_p4d_hyper,

        .alloc_pud = xen_alloc_pmd_init,
        .release_pud = xen_release_pmd_init,
#endif  /* CONFIG_X86_64 */

        .activate_mm = xen_activate_mm,
        .dup_mmap = xen_dup_mmap,
        .exit_mmap = xen_exit_mmap,

        .lazy_mode = {
                .enter = paravirt_enter_lazy_mmu,
                .leave = xen_leave_lazy_mmu,
                .flush = paravirt_flush_lazy_mmu,
        },

        .set_fixmap = xen_set_fixmap,
};

void __init xen_init_mmu_ops(void)
{
        x86_init.paging.pagetable_init = xen_pagetable_init;

        pv_mmu_ops = xen_mmu_ops;

        memset(dummy_mapping, 0xff, PAGE_SIZE);
}

/* Protected by xen_reservation_lock. */
#define MAX_CONTIG_ORDER 9 /* 2MB */
static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];

#define VOID_PTE (mfn_pte(0, __pgprot(0)))
static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
                                unsigned long *in_frames,
                                unsigned long *out_frames)
{
        int i;
        struct multicall_space mcs;

        xen_mc_batch();
        for (i = 0; i < (1UL<<order); i++, vaddr += PAGE_SIZE) {
                mcs = __xen_mc_entry(0);

                if (in_frames)
                        in_frames[i] = virt_to_mfn(vaddr);

                MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0);
                __set_phys_to_machine(virt_to_pfn(vaddr), INVALID_P2M_ENTRY);

                if (out_frames)
                        out_frames[i] = virt_to_pfn(vaddr);
        }
        xen_mc_issue(0);
}

/*
 * Update the pfn-to-mfn mappings for a virtual address range, either to
 * point to an array of mfns, or contiguously from a single starting
 * mfn.
 */
static void xen_remap_exchanged_ptes(unsigned long vaddr, int order,
                                     unsigned long *mfns,
                                     unsigned long first_mfn)
{
        unsigned i, limit;
        unsigned long mfn;

        xen_mc_batch();

        limit = 1u << order;
        for (i = 0; i < limit; i++, vaddr += PAGE_SIZE) {
                struct multicall_space mcs;
                unsigned flags;

                mcs = __xen_mc_entry(0);
                if (mfns)
                        mfn = mfns[i];
                else
                        mfn = first_mfn + i;

                if (i < (limit - 1))
                        flags = 0;
                else {
                        if (order == 0)
                                flags = UVMF_INVLPG | UVMF_ALL;
                        else
                                flags = UVMF_TLB_FLUSH | UVMF_ALL;
                }

                MULTI_update_va_mapping(mcs.mc, vaddr,
                                mfn_pte(mfn, PAGE_KERNEL), flags);

                set_phys_to_machine(virt_to_pfn(vaddr), mfn);
        }

        xen_mc_issue(0);
}

/*
 * Perform the hypercall to exchange a region of our pfns to point to
 * memory with the required contiguous alignment.  Takes the pfns as
 * input, and populates mfns as output.
 *
 * Returns a success code indicating whether the hypervisor was able to
 * satisfy the request or not.
 */
static int xen_exchange_memory(unsigned long extents_in, unsigned int order_in,
                               unsigned long *pfns_in,
                               unsigned long extents_out,
                               unsigned int order_out,
                               unsigned long *mfns_out,
                               unsigned int address_bits)
{
        long rc;
        int success;

        struct xen_memory_exchange exchange = {
                .in = {
                        .nr_extents   = extents_in,
                        .extent_order = order_in,
                        .extent_start = pfns_in,
                        .domid        = DOMID_SELF
                },
                .out = {
                        .nr_extents   = extents_out,
                        .extent_order = order_out,
                        .extent_start = mfns_out,
                        .address_bits = address_bits,
                        .domid        = DOMID_SELF
                }
        };

        BUG_ON(extents_in << order_in != extents_out << order_out);

        rc = HYPERVISOR_memory_op(XENMEM_exchange, &exchange);
        success = (exchange.nr_exchanged == extents_in);

        BUG_ON(!success && ((exchange.nr_exchanged != 0) || (rc == 0)));
        BUG_ON(success && (rc != 0));

        return success;
}

int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
                                 unsigned int address_bits,
                                 dma_addr_t *dma_handle)
{
        unsigned long *in_frames = discontig_frames, out_frame;
        unsigned long  flags;
        int            success;
        unsigned long vstart = (unsigned long)phys_to_virt(pstart);

        /*
         * Currently an auto-translated guest will not perform I/O, nor will
         * it require PAE page directories below 4GB. Therefore any calls to
         * this function are redundant and can be ignored.
         */

        if (unlikely(order > MAX_CONTIG_ORDER))
                return -ENOMEM;

        memset((void *) vstart, 0, PAGE_SIZE << order);

        spin_lock_irqsave(&xen_reservation_lock, flags);

        /* 1. Zap current PTEs, remembering MFNs. */
        xen_zap_pfn_range(vstart, order, in_frames, NULL);

        /* 2. Get a new contiguous memory extent. */
        out_frame = virt_to_pfn(vstart);
        success = xen_exchange_memory(1UL << order, 0, in_frames,
                                      1, order, &out_frame,
                                      address_bits);

        /* 3. Map the new extent in place of old pages. */
        if (success)
                xen_remap_exchanged_ptes(vstart, order, NULL, out_frame);
        else
                xen_remap_exchanged_ptes(vstart, order, in_frames, 0);

        spin_unlock_irqrestore(&xen_reservation_lock, flags);

        *dma_handle = virt_to_machine(vstart).maddr;
        return success ? 0 : -ENOMEM;
}
EXPORT_SYMBOL_GPL(xen_create_contiguous_region);

void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order)
{
        unsigned long *out_frames = discontig_frames, in_frame;
        unsigned long  flags;
        int success;
        unsigned long vstart;

        if (unlikely(order > MAX_CONTIG_ORDER))
                return;

        vstart = (unsigned long)phys_to_virt(pstart);
        memset((void *) vstart, 0, PAGE_SIZE << order);

        spin_lock_irqsave(&xen_reservation_lock, flags);

        /* 1. Find start MFN of contiguous extent. */
        in_frame = virt_to_mfn(vstart);

        /* 2. Zap current PTEs. */
        xen_zap_pfn_range(vstart, order, NULL, out_frames);

        /* 3. Do the exchange for non-contiguous MFNs. */
        success = xen_exchange_memory(1, order, &in_frame, 1UL << order,
                                        0, out_frames, 0);

        /* 4. Map new pages in place of old pages. */
        if (success)
                xen_remap_exchanged_ptes(vstart, order, out_frames, 0);
        else
                xen_remap_exchanged_ptes(vstart, order, NULL, in_frame);

        spin_unlock_irqrestore(&xen_reservation_lock, flags);
}
EXPORT_SYMBOL_GPL(xen_destroy_contiguous_region);

#ifdef CONFIG_KEXEC_CORE
phys_addr_t paddr_vmcoreinfo_note(void)
{
        if (xen_pv_domain())
                return virt_to_machine(vmcoreinfo_note).maddr;
        else
                return __pa(vmcoreinfo_note);
}
#endif /* CONFIG_KEXEC_CORE */