arch/x86/include/asm/pgtable-3level.h

   1 #ifndef _ASM_X86_PGTABLE_3LEVEL_H
   2 #define _ASM_X86_PGTABLE_3LEVEL_H
   3
   4 /*
   5  * Intel Physical Address Extension (PAE) Mode - three-level page
   6  * tables on PPro+ CPUs.
   7  *
   8  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
   9  */
  10
  11 #define pte_ERROR(e)                                                    \
  12         pr_err("%s:%d: bad pte %p(%08lx%08lx)\n",                       \
  13                __FILE__, __LINE__, &(e), (e).pte_high, (e).pte_low)
  14 #define pmd_ERROR(e)                                                    \
  15         pr_err("%s:%d: bad pmd %p(%016Lx)\n",                           \
  16                __FILE__, __LINE__, &(e), pmd_val(e))
  17 #define pgd_ERROR(e)                                                    \
  18         pr_err("%s:%d: bad pgd %p(%016Lx)\n",                           \
  19                __FILE__, __LINE__, &(e), pgd_val(e))
  20
  21 /* Rules for using set_pte: the pte being assigned *must* be
  22  * either not present or in a state where the hardware will
  23  * not attempt to update the pte.  In places where this is
  24  * not possible, use pte_get_and_clear to obtain the old pte
  25  * value and then use set_pte to update it.  -ben
  26  */
  27 static inline void native_set_pte(pte_t *ptep, pte_t pte)
  28 {
  29         ptep->pte_high = pte.pte_high;
  30         smp_wmb();
  31         ptep->pte_low = pte.pte_low;
  32 }
  33
  34 #define pmd_read_atomic pmd_read_atomic
  35 /*
  36  * pte_offset_map_lock on 32bit PAE kernels was reading the pmd_t with
  37  * a "*pmdp" dereference done by gcc. Problem is, in certain places
  38  * where pte_offset_map_lock is called, concurrent page faults are
  39  * allowed, if the mmap_sem is hold for reading. An example is mincore
  40  * vs page faults vs MADV_DONTNEED. On the page fault side
  41  * pmd_populate rightfully does a set_64bit, but if we're reading the
  42  * pmd_t with a "*pmdp" on the mincore side, a SMP race can happen
  43  * because gcc will not read the 64bit of the pmd atomically. To fix
  44  * this all places running pmd_offset_map_lock() while holding the
  45  * mmap_sem in read mode, shall read the pmdp pointer using this
  46  * function to know if the pmd is null nor not, and in turn to know if
  47  * they can run pmd_offset_map_lock or pmd_trans_huge or other pmd
  48  * operations.
  49  *
  50  * Without THP if the mmap_sem is hold for reading, the pmd can only
  51  * transition from null to not null while pmd_read_atomic runs. So
  52  * we can always return atomic pmd values with this function.
  53  *
  54  * With THP if the mmap_sem is hold for reading, the pmd can become
  55  * trans_huge or none or point to a pte (and in turn become "stable")
  56  * at any time under pmd_read_atomic. We could read it really
  57  * atomically here with a atomic64_read for the THP enabled case (and
  58  * it would be a whole lot simpler), but to avoid using cmpxchg8b we
  59  * only return an atomic pmdval if the low part of the pmdval is later
  60  * found stable (i.e. pointing to a pte). And we're returning a none
  61  * pmdval if the low part of the pmd is none. In some cases the high
  62  * and low part of the pmdval returned may not be consistent if THP is
  63  * enabled (the low part may point to previously mapped hugepage,
  64  * while the high part may point to a more recently mapped hugepage),
  65  * but pmd_none_or_trans_huge_or_clear_bad() only needs the low part
  66  * of the pmd to be read atomically to decide if the pmd is unstable
  67  * or not, with the only exception of when the low part of the pmd is
  68  * zero in which case we return a none pmd.
  69  */
  70 static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
  71 {
  72         pmdval_t ret;
  73         u32 *tmp = (u32 *)pmdp;
  74
  75         ret = (pmdval_t) (*tmp);
  76         if (ret) {
  77                 /*
  78                  * If the low part is null, we must not read the high part
  79                  * or we can end up with a partial pmd.
  80                  */
  81                 smp_rmb();
  82                 ret |= ((pmdval_t)*(tmp + 1)) << 32;
  83         }
  84
  85         return (pmd_t) { ret };
  86 }
  87
  88 static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
  89 {
  90         set_64bit((unsigned long long *)(ptep), native_pte_val(pte));
  91 }
  92
  93 static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
  94 {
  95         set_64bit((unsigned long long *)(pmdp), native_pmd_val(pmd));
  96 }
  97
  98 static inline void native_set_pud(pud_t *pudp, pud_t pud)
  99 {
 100         set_64bit((unsigned long long *)(pudp), native_pud_val(pud));
 101 }
 102
 103 /*
 104  * For PTEs and PDEs, we must clear the P-bit first when clearing a page table
 105  * entry, so clear the bottom half first and enforce ordering with a compiler
 106  * barrier.
 107  */
 108 static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr,
 109                                     pte_t *ptep)
 110 {
 111         ptep->pte_low = 0;
 112         smp_wmb();
 113         ptep->pte_high = 0;
 114 }
 115
 116 static inline void native_pmd_clear(pmd_t *pmd)
 117 {
 118         u32 *tmp = (u32 *)pmd;
 119         *tmp = 0;
 120         smp_wmb();
 121         *(tmp + 1) = 0;
 122 }
 123
 124 static inline void native_pud_clear(pud_t *pudp)
 125 {
 126 }
 127
 128 static inline void pud_clear(pud_t *pudp)
 129 {
 130         set_pud(pudp, __pud(0));
 131
 132         /*
 133          * According to Intel App note "TLBs, Paging-Structure Caches,
 134          * and Their Invalidation", April 2007, document 317080-001,
 135          * section 8.1: in PAE mode we explicitly have to flush the
 136          * TLB via cr3 if the top-level pgd is changed...
 137          *
 138          * Currently all places where pud_clear() is called either have
 139          * flush_tlb_mm() followed or don't need TLB flush (x86_64 code or
 140          * pud_clear_bad()), so we don't need TLB flush here.
 141          */
 142 }
 143
 144 #ifdef CONFIG_SMP
 145 static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
 146 {
 147         pte_t res;
 148
 149         /* xchg acts as a barrier before the setting of the high bits */
 150         res.pte_low = xchg(&ptep->pte_low, 0);
 151         res.pte_high = ptep->pte_high;
 152         ptep->pte_high = 0;
 153
 154         return res;
 155 }
 156 #else
 157 #define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
 158 #endif
 159
 160 #ifdef CONFIG_SMP
 161 union split_pmd {
 162         struct {
 163                 u32 pmd_low;
 164                 u32 pmd_high;
 165         };
 166         pmd_t pmd;
 167 };
 168 static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp)
 169 {
 170         union split_pmd res, *orig = (union split_pmd *)pmdp;
 171
 172         /* xchg acts as a barrier before setting of the high bits */
 173         res.pmd_low = xchg(&orig->pmd_low, 0);
 174         res.pmd_high = orig->pmd_high;
 175         orig->pmd_high = 0;
 176
 177         return res.pmd;
 178 }
 179 #else
 180 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
 181 #endif
 182
 183 #ifdef CONFIG_SMP
 184 union split_pud {
 185         struct {
 186                 u32 pud_low;
 187                 u32 pud_high;
 188         };
 189         pud_t pud;
 190 };
 191
 192 static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
 193 {
 194         union split_pud res, *orig = (union split_pud *)pudp;
 195
 196         /* xchg acts as a barrier before setting of the high bits */
 197         res.pud_low = xchg(&orig->pud_low, 0);
 198         res.pud_high = orig->pud_high;
 199         orig->pud_high = 0;
 200
 201         return res.pud;
 202 }
 203 #else
 204 #define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp)
 205 #endif
 206
 207 /* Encode and de-code a swap entry */
 208 #define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > 5)
 209 #define __swp_type(x)                   (((x).val) & 0x1f)
 210 #define __swp_offset(x)                 ((x).val >> 5)
 211 #define __swp_entry(type, offset)       ((swp_entry_t){(type) | (offset) << 5})
 212 #define __pte_to_swp_entry(pte)         ((swp_entry_t){ (pte).pte_high })
 213 #define __swp_entry_to_pte(x)           ((pte_t){ { .pte_high = (x).val } })
 214
 215 #define gup_get_pte gup_get_pte
 216 /*
 217  * WARNING: only to be used in the get_user_pages_fast() implementation.
 218  *
 219  * With get_user_pages_fast(), we walk down the pagetables without taking
 220  * any locks.  For this we would like to load the pointers atomically,
 221  * but that is not possible (without expensive cmpxchg8b) on PAE.  What
 222  * we do have is the guarantee that a PTE will only either go from not
 223  * present to present, or present to not present or both -- it will not
 224  * switch to a completely different present page without a TLB flush in
 225  * between; something that we are blocking by holding interrupts off.
 226  *
 227  * Setting ptes from not present to present goes:
 228  *
 229  *   ptep->pte_high = h;
 230  *   smp_wmb();
 231  *   ptep->pte_low = l;
 232  *
 233  * And present to not present goes:
 234  *
 235  *   ptep->pte_low = 0;
 236  *   smp_wmb();
 237  *   ptep->pte_high = 0;
 238  *
 239  * We must ensure here that the load of pte_low sees 'l' iff pte_high
 240  * sees 'h'. We load pte_high *after* loading pte_low, which ensures we
 241  * don't see an older value of pte_high.  *Then* we recheck pte_low,
 242  * which ensures that we haven't picked up a changed pte high. We might
 243  * have gotten rubbish values from pte_low and pte_high, but we are
 244  * guaranteed that pte_low will not have the present bit set *unless*
 245  * it is 'l'. Because get_user_pages_fast() only operates on present ptes
 246  * we're safe.
 247  */
 248 static inline pte_t gup_get_pte(pte_t *ptep)
 249 {
 250         pte_t pte;
 251
 252         do {
 253                 pte.pte_low = ptep->pte_low;
 254                 smp_rmb();
 255                 pte.pte_high = ptep->pte_high;
 256                 smp_rmb();
 257         } while (unlikely(pte.pte_low != ptep->pte_low));
 258
 259         return pte;
 260 }
 261
 262 #endif /* _ASM_X86_PGTABLE_3LEVEL_H */