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/gfp.h>
  26 #include <linux/mm.h>
  27 #include <linux/init.h>
  28 #include <linux/percpu.h>
  29 #include <linux/hardirq.h>
  30 #include <asm/pgalloc.h>
  31 #include <asm/tlbflush.h>
  32 #include <asm/tlb.h>
  33
  34 #include "mmu_decl.h"
  35
  36 DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
  37
  38 #ifdef CONFIG_SMP
  39
  40 /*
  41  * Handle batching of page table freeing on SMP. Page tables are
  42  * queued up and send to be freed later by RCU in order to avoid
  43  * freeing a page table page that is being walked without locks
  44  */
  45
  46 static DEFINE_PER_CPU(struct pte_freelist_batch *, pte_freelist_cur);
  47 static unsigned long pte_freelist_forced_free;
  48
  49 struct pte_freelist_batch
  50 {
  51         struct rcu_head rcu;
  52         unsigned int    index;
  53         unsigned long   tables[0];
  54 };
  55
  56 #define PTE_FREELIST_SIZE \
  57         ((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
  58           / sizeof(unsigned long))
  59
  60 static void pte_free_smp_sync(void *arg)
  61 {
  62         /* Do nothing, just ensure we sync with all CPUs */
  63 }
  64
  65 /* This is only called when we are critically out of memory
  66  * (and fail to get a page in pte_free_tlb).
  67  */
  68 static void pgtable_free_now(void *table, unsigned shift)
  69 {
  70         pte_freelist_forced_free++;
  71
  72         smp_call_function(pte_free_smp_sync, NULL, 1);
  73
  74         pgtable_free(table, shift);
  75 }
  76
  77 static void pte_free_rcu_callback(struct rcu_head *head)
  78 {
  79         struct pte_freelist_batch *batch =
  80                 container_of(head, struct pte_freelist_batch, rcu);
  81         unsigned int i;
  82
  83         for (i = 0; i < batch->index; i++) {
  84                 void *table = (void *)(batch->tables[i] & ~MAX_PGTABLE_INDEX_SIZE);
  85                 unsigned shift = batch->tables[i] & MAX_PGTABLE_INDEX_SIZE;
  86
  87                 pgtable_free(table, shift);
  88         }
  89
  90         free_page((unsigned long)batch);
  91 }
  92
  93 static void pte_free_submit(struct pte_freelist_batch *batch)
  94 {
  95         INIT_RCU_HEAD(&batch->rcu);
  96         call_rcu(&batch->rcu, pte_free_rcu_callback);
  97 }
  98
  99 void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift)
 100 {
 101         /* This is safe since tlb_gather_mmu has disabled preemption */
 102         struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
 103         unsigned long pgf;
 104
 105         if (atomic_read(&tlb->mm->mm_users) < 2 ||
 106             cpumask_equal(mm_cpumask(tlb->mm), cpumask_of(smp_processor_id()))){
 107                 pgtable_free(table, shift);
 108                 return;
 109         }
 110
 111         if (*batchp == NULL) {
 112                 *batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
 113                 if (*batchp == NULL) {
 114                         pgtable_free_now(table, shift);
 115                         return;
 116                 }
 117                 (*batchp)->index = 0;
 118         }
 119         BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
 120         pgf = (unsigned long)table | shift;
 121         (*batchp)->tables[(*batchp)->index++] = pgf;
 122         if ((*batchp)->index == PTE_FREELIST_SIZE) {
 123                 pte_free_submit(*batchp);
 124                 *batchp = NULL;
 125         }
 126 }
 127
 128 void pte_free_finish(void)
 129 {
 130         /* This is safe since tlb_gather_mmu has disabled preemption */
 131         struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
 132
 133         if (*batchp == NULL)
 134                 return;
 135         pte_free_submit(*batchp);
 136         *batchp = NULL;
 137 }
 138
 139 #endif /* CONFIG_SMP */
 140
 141 static inline int is_exec_fault(void)
 142 {
 143         return current->thread.regs && TRAP(current->thread.regs) == 0x400;
 144 }
 145
 146 /* We only try to do i/d cache coherency on stuff that looks like
 147  * reasonably "normal" PTEs. We currently require a PTE to be present
 148  * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
 149  * on userspace PTEs
 150  */
 151 static inline int pte_looks_normal(pte_t pte)
 152 {
 153         return (pte_val(pte) &
 154             (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
 155             (_PAGE_PRESENT | _PAGE_USER);
 156 }
 157
 158 struct page * maybe_pte_to_page(pte_t pte)
 159 {
 160         unsigned long pfn = pte_pfn(pte);
 161         struct page *page;
 162
 163         if (unlikely(!pfn_valid(pfn)))
 164                 return NULL;
 165         page = pfn_to_page(pfn);
 166         if (PageReserved(page))
 167                 return NULL;
 168         return page;
 169 }
 170
 171 #if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0
 172
 173 /* Server-style MMU handles coherency when hashing if HW exec permission
 174  * is supposed per page (currently 64-bit only). If not, then, we always
 175  * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
 176  * support falls into the same category.
 177  */
 178
 179 static pte_t set_pte_filter(pte_t pte, unsigned long addr)
 180 {
 181         pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
 182         if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
 183                                        cpu_has_feature(CPU_FTR_NOEXECUTE))) {
 184                 struct page *pg = maybe_pte_to_page(pte);
 185                 if (!pg)
 186                         return pte;
 187                 if (!test_bit(PG_arch_1, &pg->flags)) {
 188 #ifdef CONFIG_8xx
 189                         /* On 8xx, cache control instructions (particularly
 190                          * "dcbst" from flush_dcache_icache) fault as write
 191                          * operation if there is an unpopulated TLB entry
 192                          * for the address in question. To workaround that,
 193                          * we invalidate the TLB here, thus avoiding dcbst
 194                          * misbehaviour.
 195                          */
 196                         /* 8xx doesn't care about PID, size or ind args */
 197                         _tlbil_va(addr, 0, 0, 0);
 198 #endif /* CONFIG_8xx */
 199                         flush_dcache_icache_page(pg);
 200                         set_bit(PG_arch_1, &pg->flags);
 201                 }
 202         }
 203         return pte;
 204 }
 205
 206 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 207                                      int dirty)
 208 {
 209         return pte;
 210 }
 211
 212 #else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */
 213
 214 /* Embedded type MMU with HW exec support. This is a bit more complicated
 215  * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
 216  * instead we "filter out" the exec permission for non clean pages.
 217  */
 218 static pte_t set_pte_filter(pte_t pte, unsigned long addr)
 219 {
 220         struct page *pg;
 221
 222         /* No exec permission in the first place, move on */
 223         if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
 224                 return pte;
 225
 226         /* If you set _PAGE_EXEC on weird pages you're on your own */
 227         pg = maybe_pte_to_page(pte);
 228         if (unlikely(!pg))
 229                 return pte;
 230
 231         /* If the page clean, we move on */
 232         if (test_bit(PG_arch_1, &pg->flags))
 233                 return pte;
 234
 235         /* If it's an exec fault, we flush the cache and make it clean */
 236         if (is_exec_fault()) {
 237                 flush_dcache_icache_page(pg);
 238                 set_bit(PG_arch_1, &pg->flags);
 239                 return pte;
 240         }
 241
 242         /* Else, we filter out _PAGE_EXEC */
 243         return __pte(pte_val(pte) & ~_PAGE_EXEC);
 244 }
 245
 246 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 247                                      int dirty)
 248 {
 249         struct page *pg;
 250
 251         /* So here, we only care about exec faults, as we use them
 252          * to recover lost _PAGE_EXEC and perform I$/D$ coherency
 253          * if necessary. Also if _PAGE_EXEC is already set, same deal,
 254          * we just bail out
 255          */
 256         if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
 257                 return pte;
 258
 259 #ifdef CONFIG_DEBUG_VM
 260         /* So this is an exec fault, _PAGE_EXEC is not set. If it was
 261          * an error we would have bailed out earlier in do_page_fault()
 262          * but let's make sure of it
 263          */
 264         if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
 265                 return pte;
 266 #endif /* CONFIG_DEBUG_VM */
 267
 268         /* If you set _PAGE_EXEC on weird pages you're on your own */
 269         pg = maybe_pte_to_page(pte);
 270         if (unlikely(!pg))
 271                 goto bail;
 272
 273         /* If the page is already clean, we move on */
 274         if (test_bit(PG_arch_1, &pg->flags))
 275                 goto bail;
 276
 277         /* Clean the page and set PG_arch_1 */
 278         flush_dcache_icache_page(pg);
 279         set_bit(PG_arch_1, &pg->flags);
 280
 281  bail:
 282         return __pte(pte_val(pte) | _PAGE_EXEC);
 283 }
 284
 285 #endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */
 286
 287 /*
 288  * set_pte stores a linux PTE into the linux page table.
 289  */
 290 void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
 291                 pte_t pte)
 292 {
 293 #ifdef CONFIG_DEBUG_VM
 294         WARN_ON(pte_present(*ptep));
 295 #endif
 296         /* Note: mm->context.id might not yet have been assigned as
 297          * this context might not have been activated yet when this
 298          * is called.
 299          */
 300         pte = set_pte_filter(pte, addr);
 301
 302         /* Perform the setting of the PTE */
 303         __set_pte_at(mm, addr, ptep, pte, 0);
 304 }
 305
 306 /*
 307  * This is called when relaxing access to a PTE. It's also called in the page
 308  * fault path when we don't hit any of the major fault cases, ie, a minor
 309  * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
 310  * handled those two for us, we additionally deal with missing execute
 311  * permission here on some processors
 312  */
 313 int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
 314                           pte_t *ptep, pte_t entry, int dirty)
 315 {
 316         int changed;
 317         entry = set_access_flags_filter(entry, vma, dirty);
 318         changed = !pte_same(*(ptep), entry);
 319         if (changed) {
 320                 if (!(vma->vm_flags & VM_HUGETLB))
 321                         assert_pte_locked(vma->vm_mm, address);
 322                 __ptep_set_access_flags(ptep, entry);
 323                 flush_tlb_page_nohash(vma, address);
 324         }
 325         return changed;
 326 }
 327
 328 #ifdef CONFIG_DEBUG_VM
 329 void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 330 {
 331         pgd_t *pgd;
 332         pud_t *pud;
 333         pmd_t *pmd;
 334
 335         if (mm == &init_mm)
 336                 return;
 337         pgd = mm->pgd + pgd_index(addr);
 338         BUG_ON(pgd_none(*pgd));
 339         pud = pud_offset(pgd, addr);
 340         BUG_ON(pud_none(*pud));
 341         pmd = pmd_offset(pud, addr);
 342         BUG_ON(!pmd_present(*pmd));
 343         assert_spin_locked(pte_lockptr(mm, pmd));
 344 }
 345 #endif /* CONFIG_DEBUG_VM */
 346