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/percpu.h>
  28 #include <linux/hardirq.h>
  29 #include <linux/hugetlb.h>
  30 #include <asm/pgalloc.h>
  31 #include <asm/tlbflush.h>
  32 #include <asm/tlb.h>
  33
  34 static inline int is_exec_fault(void)
  35 {
  36         return current->thread.regs && TRAP(current->thread.regs) == 0x400;
  37 }
  38
  39 /* We only try to do i/d cache coherency on stuff that looks like
  40  * reasonably "normal" PTEs. We currently require a PTE to be present
  41  * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
  42  * on userspace PTEs
  43  */
  44 static inline int pte_looks_normal(pte_t pte)
  45 {
  46         return (pte_val(pte) &
  47             (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
  48             (_PAGE_PRESENT | _PAGE_USER);
  49 }
  50
  51 struct page * maybe_pte_to_page(pte_t pte)
  52 {
  53         unsigned long pfn = pte_pfn(pte);
  54         struct page *page;
  55
  56         if (unlikely(!pfn_valid(pfn)))
  57                 return NULL;
  58         page = pfn_to_page(pfn);
  59         if (PageReserved(page))
  60                 return NULL;
  61         return page;
  62 }
  63
  64 #if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0
  65
  66 /* Server-style MMU handles coherency when hashing if HW exec permission
  67  * is supposed per page (currently 64-bit only). If not, then, we always
  68  * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
  69  * support falls into the same category.
  70  */
  71
  72 static pte_t set_pte_filter(pte_t pte)
  73 {
  74         pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
  75         if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
  76                                        cpu_has_feature(CPU_FTR_NOEXECUTE))) {
  77                 struct page *pg = maybe_pte_to_page(pte);
  78                 if (!pg)
  79                         return pte;
  80                 if (!test_bit(PG_arch_1, &pg->flags)) {
  81                         flush_dcache_icache_page(pg);
  82                         set_bit(PG_arch_1, &pg->flags);
  83                 }
  84         }
  85         return pte;
  86 }
  87
  88 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
  89                                      int dirty)
  90 {
  91         return pte;
  92 }
  93
  94 #else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */
  95
  96 /* Embedded type MMU with HW exec support. This is a bit more complicated
  97  * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
  98  * instead we "filter out" the exec permission for non clean pages.
  99  */
 100 static pte_t set_pte_filter(pte_t pte)
 101 {
 102         struct page *pg;
 103
 104         /* No exec permission in the first place, move on */
 105         if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
 106                 return pte;
 107
 108         /* If you set _PAGE_EXEC on weird pages you're on your own */
 109         pg = maybe_pte_to_page(pte);
 110         if (unlikely(!pg))
 111                 return pte;
 112
 113         /* If the page clean, we move on */
 114         if (test_bit(PG_arch_1, &pg->flags))
 115                 return pte;
 116
 117         /* If it's an exec fault, we flush the cache and make it clean */
 118         if (is_exec_fault()) {
 119                 flush_dcache_icache_page(pg);
 120                 set_bit(PG_arch_1, &pg->flags);
 121                 return pte;
 122         }
 123
 124         /* Else, we filter out _PAGE_EXEC */
 125         return __pte(pte_val(pte) & ~_PAGE_EXEC);
 126 }
 127
 128 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 129                                      int dirty)
 130 {
 131         struct page *pg;
 132
 133         /* So here, we only care about exec faults, as we use them
 134          * to recover lost _PAGE_EXEC and perform I$/D$ coherency
 135          * if necessary. Also if _PAGE_EXEC is already set, same deal,
 136          * we just bail out
 137          */
 138         if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
 139                 return pte;
 140
 141 #ifdef CONFIG_DEBUG_VM
 142         /* So this is an exec fault, _PAGE_EXEC is not set. If it was
 143          * an error we would have bailed out earlier in do_page_fault()
 144          * but let's make sure of it
 145          */
 146         if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
 147                 return pte;
 148 #endif /* CONFIG_DEBUG_VM */
 149
 150         /* If you set _PAGE_EXEC on weird pages you're on your own */
 151         pg = maybe_pte_to_page(pte);
 152         if (unlikely(!pg))
 153                 goto bail;
 154
 155         /* If the page is already clean, we move on */
 156         if (test_bit(PG_arch_1, &pg->flags))
 157                 goto bail;
 158
 159         /* Clean the page and set PG_arch_1 */
 160         flush_dcache_icache_page(pg);
 161         set_bit(PG_arch_1, &pg->flags);
 162
 163  bail:
 164         return __pte(pte_val(pte) | _PAGE_EXEC);
 165 }
 166
 167 #endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */
 168
 169 /*
 170  * set_pte stores a linux PTE into the linux page table.
 171  */
 172 void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
 173                 pte_t pte)
 174 {
 175 #ifdef CONFIG_DEBUG_VM
 176         WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
 177 #endif
 178         /* Note: mm->context.id might not yet have been assigned as
 179          * this context might not have been activated yet when this
 180          * is called.
 181          */
 182         pte = set_pte_filter(pte);
 183
 184         /* Perform the setting of the PTE */
 185         __set_pte_at(mm, addr, ptep, pte, 0);
 186 }
 187
 188 /*
 189  * This is called when relaxing access to a PTE. It's also called in the page
 190  * fault path when we don't hit any of the major fault cases, ie, a minor
 191  * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
 192  * handled those two for us, we additionally deal with missing execute
 193  * permission here on some processors
 194  */
 195 int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
 196                           pte_t *ptep, pte_t entry, int dirty)
 197 {
 198         int changed;
 199         entry = set_access_flags_filter(entry, vma, dirty);
 200         changed = !pte_same(*(ptep), entry);
 201         if (changed) {
 202                 if (!is_vm_hugetlb_page(vma))
 203                         assert_pte_locked(vma->vm_mm, address);
 204                 __ptep_set_access_flags(ptep, entry);
 205                 flush_tlb_page_nohash(vma, address);
 206         }
 207         return changed;
 208 }
 209
 210 #ifdef CONFIG_DEBUG_VM
 211 void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 212 {
 213         pgd_t *pgd;
 214         pud_t *pud;
 215         pmd_t *pmd;
 216
 217         if (mm == &init_mm)
 218                 return;
 219         pgd = mm->pgd + pgd_index(addr);
 220         BUG_ON(pgd_none(*pgd));
 221         pud = pud_offset(pgd, addr);
 222         BUG_ON(pud_none(*pud));
 223         pmd = pmd_offset(pud, addr);
 224         /*
 225          * khugepaged to collapse normal pages to hugepage, first set
 226          * pmd to none to force page fault/gup to take mmap_sem. After
 227          * pmd is set to none, we do a pte_clear which does this assertion
 228          * so if we find pmd none, return.
 229          */
 230         if (pmd_none(*pmd))
 231                 return;
 232         BUG_ON(!pmd_present(*pmd));
 233         assert_spin_locked(pte_lockptr(mm, pmd));
 234 }
 235 #endif /* CONFIG_DEBUG_VM */
 236