Documentation/filesystems/vfs.txt: fix ->repeasepage() description

[linux-2.6/next.git] / arch / powerpc / mm / pgtable.c

/*
 * This file contains common routines for dealing with free of page tables
 * Along with common page table handling code
 *
 *  Derived from arch/powerpc/mm/tlb_64.c:
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
 *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
 *    Copyright (C) 1996 Paul Mackerras
 *
 *  Derived from "arch/i386/mm/init.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Dave Engebretsen <engebret@us.ibm.com>
 *      Rework for PPC64 port.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>

#include "mmu_decl.h"

DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);

#ifdef CONFIG_SMP

/*
 * Handle batching of page table freeing on SMP. Page tables are
 * queued up and send to be freed later by RCU in order to avoid
 * freeing a page table page that is being walked without locks
 */

static DEFINE_PER_CPU(struct pte_freelist_batch *, pte_freelist_cur);
static unsigned long pte_freelist_forced_free;

struct pte_freelist_batch
{
        struct rcu_head rcu;
        unsigned int    index;
        unsigned long   tables[0];
};

#define PTE_FREELIST_SIZE \
        ((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
          / sizeof(unsigned long))

static void pte_free_smp_sync(void *arg)
{
        /* Do nothing, just ensure we sync with all CPUs */
}

/* This is only called when we are critically out of memory
 * (and fail to get a page in pte_free_tlb).
 */
static void pgtable_free_now(void *table, unsigned shift)
{
        pte_freelist_forced_free++;

        smp_call_function(pte_free_smp_sync, NULL, 1);

        pgtable_free(table, shift);
}

static void pte_free_rcu_callback(struct rcu_head *head)
{
        struct pte_freelist_batch *batch =
                container_of(head, struct pte_freelist_batch, rcu);
        unsigned int i;

        for (i = 0; i < batch->index; i++) {
                void *table = (void *)(batch->tables[i] & ~MAX_PGTABLE_INDEX_SIZE);
                unsigned shift = batch->tables[i] & MAX_PGTABLE_INDEX_SIZE;

                pgtable_free(table, shift);
        }

        free_page((unsigned long)batch);
}

static void pte_free_submit(struct pte_freelist_batch *batch)
{
        call_rcu_sched(&batch->rcu, pte_free_rcu_callback);
}

void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift)
{
        /* This is safe since tlb_gather_mmu has disabled preemption */
        struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
        unsigned long pgf;

        if (atomic_read(&tlb->mm->mm_users) < 2 ||
            cpumask_equal(mm_cpumask(tlb->mm), cpumask_of(smp_processor_id()))){
                pgtable_free(table, shift);
                return;
        }

        if (*batchp == NULL) {
                *batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
                if (*batchp == NULL) {
                        pgtable_free_now(table, shift);
                        return;
                }
                (*batchp)->index = 0;
        }
        BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
        pgf = (unsigned long)table | shift;
        (*batchp)->tables[(*batchp)->index++] = pgf;
        if ((*batchp)->index == PTE_FREELIST_SIZE) {
                pte_free_submit(*batchp);
                *batchp = NULL;
        }
}

void pte_free_finish(void)
{
        /* This is safe since tlb_gather_mmu has disabled preemption */
        struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);

        if (*batchp == NULL)
                return;
        pte_free_submit(*batchp);
        *batchp = NULL;
}

#endif /* CONFIG_SMP */

static inline int is_exec_fault(void)
{
        return current->thread.regs && TRAP(current->thread.regs) == 0x400;
}

/* We only try to do i/d cache coherency on stuff that looks like
 * reasonably "normal" PTEs. We currently require a PTE to be present
 * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
 * on userspace PTEs
 */
static inline int pte_looks_normal(pte_t pte)
{
        return (pte_val(pte) &
            (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
            (_PAGE_PRESENT | _PAGE_USER);
}

struct page * maybe_pte_to_page(pte_t pte)
{
        unsigned long pfn = pte_pfn(pte);
        struct page *page;

        if (unlikely(!pfn_valid(pfn)))
                return NULL;
        page = pfn_to_page(pfn);
        if (PageReserved(page))
                return NULL;
        return page;
}

#if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0

/* Server-style MMU handles coherency when hashing if HW exec permission
 * is supposed per page (currently 64-bit only). If not, then, we always
 * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
 * support falls into the same category.
 */

static pte_t set_pte_filter(pte_t pte, unsigned long addr)
{
        pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
        if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
                                       cpu_has_feature(CPU_FTR_NOEXECUTE))) {
                struct page *pg = maybe_pte_to_page(pte);
                if (!pg)
                        return pte;
                if (!test_bit(PG_arch_1, &pg->flags)) {
#ifdef CONFIG_8xx
                        /* On 8xx, cache control instructions (particularly
                         * "dcbst" from flush_dcache_icache) fault as write
                         * operation if there is an unpopulated TLB entry
                         * for the address in question. To workaround that,
                         * we invalidate the TLB here, thus avoiding dcbst
                         * misbehaviour.
                         */
                        /* 8xx doesn't care about PID, size or ind args */
                        _tlbil_va(addr, 0, 0, 0);
#endif /* CONFIG_8xx */
                        flush_dcache_icache_page(pg);
                        set_bit(PG_arch_1, &pg->flags);
                }
        }
        return pte;
}

static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
                                     int dirty)
{
        return pte;
}

#else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */

/* Embedded type MMU with HW exec support. This is a bit more complicated
 * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
 * instead we "filter out" the exec permission for non clean pages.
 */
static pte_t set_pte_filter(pte_t pte, unsigned long addr)
{
        struct page *pg;

        /* No exec permission in the first place, move on */
        if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
                return pte;

        /* If you set _PAGE_EXEC on weird pages you're on your own */
        pg = maybe_pte_to_page(pte);
        if (unlikely(!pg))
                return pte;

        /* If the page clean, we move on */
        if (test_bit(PG_arch_1, &pg->flags))
                return pte;

        /* If it's an exec fault, we flush the cache and make it clean */
        if (is_exec_fault()) {
                flush_dcache_icache_page(pg);
                set_bit(PG_arch_1, &pg->flags);
                return pte;
        }

        /* Else, we filter out _PAGE_EXEC */
        return __pte(pte_val(pte) & ~_PAGE_EXEC);
}

static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
                                     int dirty)
{
        struct page *pg;

        /* So here, we only care about exec faults, as we use them
         * to recover lost _PAGE_EXEC and perform I$/D$ coherency
         * if necessary. Also if _PAGE_EXEC is already set, same deal,
         * we just bail out
         */
        if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
                return pte;

#ifdef CONFIG_DEBUG_VM
        /* So this is an exec fault, _PAGE_EXEC is not set. If it was
         * an error we would have bailed out earlier in do_page_fault()
         * but let's make sure of it
         */
        if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
                return pte;
#endif /* CONFIG_DEBUG_VM */

        /* If you set _PAGE_EXEC on weird pages you're on your own */
        pg = maybe_pte_to_page(pte);
        if (unlikely(!pg))
                goto bail;

        /* If the page is already clean, we move on */
        if (test_bit(PG_arch_1, &pg->flags))
                goto bail;

        /* Clean the page and set PG_arch_1 */
        flush_dcache_icache_page(pg);
        set_bit(PG_arch_1, &pg->flags);

 bail:
        return __pte(pte_val(pte) | _PAGE_EXEC);
}

#endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */

/*
 * set_pte stores a linux PTE into the linux page table.
 */
void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
                pte_t pte)
{
#ifdef CONFIG_DEBUG_VM
        WARN_ON(pte_present(*ptep));
#endif
        /* Note: mm->context.id might not yet have been assigned as
         * this context might not have been activated yet when this
         * is called.
         */
        pte = set_pte_filter(pte, addr);

        /* Perform the setting of the PTE */
        __set_pte_at(mm, addr, ptep, pte, 0);
}

/*
 * This is called when relaxing access to a PTE. It's also called in the page
 * fault path when we don't hit any of the major fault cases, ie, a minor
 * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
 * handled those two for us, we additionally deal with missing execute
 * permission here on some processors
 */
int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
                          pte_t *ptep, pte_t entry, int dirty)
{
        int changed;
        entry = set_access_flags_filter(entry, vma, dirty);
        changed = !pte_same(*(ptep), entry);
        if (changed) {
                if (!(vma->vm_flags & VM_HUGETLB))
                        assert_pte_locked(vma->vm_mm, address);
                __ptep_set_access_flags(ptep, entry);
                flush_tlb_page_nohash(vma, address);
        }
        return changed;
}

#ifdef CONFIG_DEBUG_VM
void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;

        if (mm == &init_mm)
                return;
        pgd = mm->pgd + pgd_index(addr);
        BUG_ON(pgd_none(*pgd));
        pud = pud_offset(pgd, addr);
        BUG_ON(pud_none(*pud));
        pmd = pmd_offset(pud, addr);
        BUG_ON(!pmd_present(*pmd));
        assert_spin_locked(pte_lockptr(mm, pmd));
}
#endif /* CONFIG_DEBUG_VM */