arch/powerpc/mm/pgtable.c

   1 /*
   2  * This file contains common routines for dealing with free of page tables
   3  * Along with common page table handling code
   4  *
   5  *  Derived from arch/powerpc/mm/tlb_64.c:
   6  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
   7  *
   8  *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
   9  *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
  10  *    Copyright (C) 1996 Paul Mackerras
  11  *
  12  *  Derived from "arch/i386/mm/init.c"
  13  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  14  *
  15  *  Dave Engebretsen <engebret@us.ibm.com>
  16  *      Rework for PPC64 port.
  17  *
  18  *  This program is free software; you can redistribute it and/or
  19  *  modify it under the terms of the GNU General Public License
  20  *  as published by the Free Software Foundation; either version
  21  *  2 of the License, or (at your option) any later version.
  22  */
  23
  24 #include <linux/kernel.h>
  25 #include <linux/mm.h>
  26 #include <linux/init.h>
  27 #include <linux/percpu.h>
  28 #include <linux/hardirq.h>
  29 #include <asm/pgalloc.h>
  30 #include <asm/tlbflush.h>
  31 #include <asm/tlb.h>
  32
  33 DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
  34
  35 #ifdef CONFIG_SMP
  36
  37 /*
  38  * Handle batching of page table freeing on SMP. Page tables are
  39  * queued up and send to be freed later by RCU in order to avoid
  40  * freeing a page table page that is being walked without locks
  41  */
  42
  43 static DEFINE_PER_CPU(struct pte_freelist_batch *, pte_freelist_cur);
  44 static unsigned long pte_freelist_forced_free;
  45
  46 struct pte_freelist_batch
  47 {
  48         struct rcu_head rcu;
  49         unsigned int    index;
  50         pgtable_free_t  tables[0];
  51 };
  52
  53 #define PTE_FREELIST_SIZE \
  54         ((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
  55           / sizeof(pgtable_free_t))
  56
  57 static void pte_free_smp_sync(void *arg)
  58 {
  59         /* Do nothing, just ensure we sync with all CPUs */
  60 }
  61
  62 /* This is only called when we are critically out of memory
  63  * (and fail to get a page in pte_free_tlb).
  64  */
  65 static void pgtable_free_now(pgtable_free_t pgf)
  66 {
  67         pte_freelist_forced_free++;
  68
  69         smp_call_function(pte_free_smp_sync, NULL, 1);
  70
  71         pgtable_free(pgf);
  72 }
  73
  74 static void pte_free_rcu_callback(struct rcu_head *head)
  75 {
  76         struct pte_freelist_batch *batch =
  77                 container_of(head, struct pte_freelist_batch, rcu);
  78         unsigned int i;
  79
  80         for (i = 0; i < batch->index; i++)
  81                 pgtable_free(batch->tables[i]);
  82
  83         free_page((unsigned long)batch);
  84 }
  85
  86 static void pte_free_submit(struct pte_freelist_batch *batch)
  87 {
  88         INIT_RCU_HEAD(&batch->rcu);
  89         call_rcu(&batch->rcu, pte_free_rcu_callback);
  90 }
  91
  92 void pgtable_free_tlb(struct mmu_gather *tlb, pgtable_free_t pgf)
  93 {
  94         /* This is safe since tlb_gather_mmu has disabled preemption */
  95         struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
  96
  97         if (atomic_read(&tlb->mm->mm_users) < 2 ||
  98             cpumask_equal(mm_cpumask(tlb->mm), cpumask_of(smp_processor_id()))){
  99                 pgtable_free(pgf);
 100                 return;
 101         }
 102
 103         if (*batchp == NULL) {
 104                 *batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
 105                 if (*batchp == NULL) {
 106                         pgtable_free_now(pgf);
 107                         return;
 108                 }
 109                 (*batchp)->index = 0;
 110         }
 111         (*batchp)->tables[(*batchp)->index++] = pgf;
 112         if ((*batchp)->index == PTE_FREELIST_SIZE) {
 113                 pte_free_submit(*batchp);
 114                 *batchp = NULL;
 115         }
 116 }
 117
 118 void pte_free_finish(void)
 119 {
 120         /* This is safe since tlb_gather_mmu has disabled preemption */
 121         struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
 122
 123         if (*batchp == NULL)
 124                 return;
 125         pte_free_submit(*batchp);
 126         *batchp = NULL;
 127 }
 128
 129 #endif /* CONFIG_SMP */
 130
 131 static inline int is_exec_fault(void)
 132 {
 133         return current->thread.regs && TRAP(current->thread.regs) == 0x400;
 134 }
 135
 136 /* We only try to do i/d cache coherency on stuff that looks like
 137  * reasonably "normal" PTEs. We currently require a PTE to be present
 138  * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
 139  * on userspace PTEs
 140  */
 141 static inline int pte_looks_normal(pte_t pte)
 142 {
 143         return (pte_val(pte) &
 144             (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
 145             (_PAGE_PRESENT | _PAGE_USER);
 146 }
 147
 148 struct page * maybe_pte_to_page(pte_t pte)
 149 {
 150         unsigned long pfn = pte_pfn(pte);
 151         struct page *page;
 152
 153         if (unlikely(!pfn_valid(pfn)))
 154                 return NULL;
 155         page = pfn_to_page(pfn);
 156         if (PageReserved(page))
 157                 return NULL;
 158         return page;
 159 }
 160
 161 #if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0
 162
 163 /* Server-style MMU handles coherency when hashing if HW exec permission
 164  * is supposed per page (currently 64-bit only). If not, then, we always
 165  * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
 166  * support falls into the same category.
 167  */
 168
 169 static pte_t set_pte_filter(pte_t pte)
 170 {
 171         pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
 172         if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
 173                                        cpu_has_feature(CPU_FTR_NOEXECUTE))) {
 174                 struct page *pg = maybe_pte_to_page(pte);
 175                 if (!pg)
 176                         return pte;
 177                 if (!test_bit(PG_arch_1, &pg->flags)) {
 178                         flush_dcache_icache_page(pg);
 179                         set_bit(PG_arch_1, &pg->flags);
 180                 }
 181         }
 182         return pte;
 183 }
 184
 185 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 186                                      int dirty)
 187 {
 188         return pte;
 189 }
 190
 191 #else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */
 192
 193 /* Embedded type MMU with HW exec support. This is a bit more complicated
 194  * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
 195  * instead we "filter out" the exec permission for non clean pages.
 196  */
 197 static pte_t set_pte_filter(pte_t pte)
 198 {
 199         struct page *pg;
 200
 201         /* No exec permission in the first place, move on */
 202         if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
 203                 return pte;
 204
 205         /* If you set _PAGE_EXEC on weird pages you're on your own */
 206         pg = maybe_pte_to_page(pte);
 207         if (unlikely(!pg))
 208                 return pte;
 209
 210         /* If the page clean, we move on */
 211         if (test_bit(PG_arch_1, &pg->flags))
 212                 return pte;
 213
 214         /* If it's an exec fault, we flush the cache and make it clean */
 215         if (is_exec_fault()) {
 216                 flush_dcache_icache_page(pg);
 217                 set_bit(PG_arch_1, &pg->flags);
 218                 return pte;
 219         }
 220
 221         /* Else, we filter out _PAGE_EXEC */
 222         return __pte(pte_val(pte) & ~_PAGE_EXEC);
 223 }
 224
 225 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 226                                      int dirty)
 227 {
 228         struct page *pg;
 229
 230         /* So here, we only care about exec faults, as we use them
 231          * to recover lost _PAGE_EXEC and perform I$/D$ coherency
 232          * if necessary. Also if _PAGE_EXEC is already set, same deal,
 233          * we just bail out
 234          */
 235         if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
 236                 return pte;
 237
 238 #ifdef CONFIG_DEBUG_VM
 239         /* So this is an exec fault, _PAGE_EXEC is not set. If it was
 240          * an error we would have bailed out earlier in do_page_fault()
 241          * but let's make sure of it
 242          */
 243         if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
 244                 return pte;
 245 #endif /* CONFIG_DEBUG_VM */
 246
 247         /* If you set _PAGE_EXEC on weird pages you're on your own */
 248         pg = maybe_pte_to_page(pte);
 249         if (unlikely(!pg))
 250                 goto bail;
 251
 252         /* If the page is already clean, we move on */
 253         if (test_bit(PG_arch_1, &pg->flags))
 254                 goto bail;
 255
 256         /* Clean the page and set PG_arch_1 */
 257         flush_dcache_icache_page(pg);
 258         set_bit(PG_arch_1, &pg->flags);
 259
 260  bail:
 261         return __pte(pte_val(pte) | _PAGE_EXEC);
 262 }
 263
 264 #endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */
 265
 266 /*
 267  * set_pte stores a linux PTE into the linux page table.
 268  */
 269 void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
 270                 pte_t pte)
 271 {
 272 #ifdef CONFIG_DEBUG_VM
 273         WARN_ON(pte_present(*ptep));
 274 #endif
 275         /* Note: mm->context.id might not yet have been assigned as
 276          * this context might not have been activated yet when this
 277          * is called.
 278          */
 279         pte = set_pte_filter(pte);
 280
 281         /* Perform the setting of the PTE */
 282         __set_pte_at(mm, addr, ptep, pte, 0);
 283 }
 284
 285 /*
 286  * This is called when relaxing access to a PTE. It's also called in the page
 287  * fault path when we don't hit any of the major fault cases, ie, a minor
 288  * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
 289  * handled those two for us, we additionally deal with missing execute
 290  * permission here on some processors
 291  */
 292 int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
 293                           pte_t *ptep, pte_t entry, int dirty)
 294 {
 295         int changed;
 296         entry = set_access_flags_filter(entry, vma, dirty);
 297         changed = !pte_same(*(ptep), entry);
 298         if (changed) {
 299                 if (!(vma->vm_flags & VM_HUGETLB))
 300                         assert_pte_locked(vma->vm_mm, address);
 301                 __ptep_set_access_flags(ptep, entry);
 302                 flush_tlb_page_nohash(vma, address);
 303         }
 304         return changed;
 305 }
 306
 307 #ifdef CONFIG_DEBUG_VM
 308 void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 309 {
 310         pgd_t *pgd;
 311         pud_t *pud;
 312         pmd_t *pmd;
 313
 314         if (mm == &init_mm)
 315                 return;
 316         pgd = mm->pgd + pgd_index(addr);
 317         BUG_ON(pgd_none(*pgd));
 318         pud = pud_offset(pgd, addr);
 319         BUG_ON(pud_none(*pud));
 320         pmd = pmd_offset(pud, addr);
 321         BUG_ON(!pmd_present(*pmd));
 322         assert_spin_locked(pte_lockptr(mm, pmd));
 323 }
 324 #endif /* CONFIG_DEBUG_VM */
 325