1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _ASM_X86_PGTABLE_3LEVEL_H 3 #define _ASM_X86_PGTABLE_3LEVEL_H 4 5 /* 6 * Intel Physical Address Extension (PAE) Mode - three-level page 7 * tables on PPro+ CPUs. 8 * 9 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com> 10 */ 11 12 #define pte_ERROR(e) \ 13 pr_err("%s:%d: bad pte %p(%08lx%08lx)\n", \ 14 __FILE__, __LINE__, &(e), (e).pte_high, (e).pte_low) 15 #define pmd_ERROR(e) \ 16 pr_err("%s:%d: bad pmd %p(%016Lx)\n", \ 17 __FILE__, __LINE__, &(e), pmd_val(e)) 18 #define pgd_ERROR(e) \ 19 pr_err("%s:%d: bad pgd %p(%016Lx)\n", \ 20 __FILE__, __LINE__, &(e), pgd_val(e)) 21 22 /* Rules for using set_pte: the pte being assigned *must* be 23 * either not present or in a state where the hardware will 24 * not attempt to update the pte. In places where this is 25 * not possible, use pte_get_and_clear to obtain the old pte 26 * value and then use set_pte to update it. -ben 27 */ 28 static inline void native_set_pte(pte_t *ptep, pte_t pte) 29 { 30 ptep->pte_high = pte.pte_high; 31 smp_wmb(); 32 ptep->pte_low = pte.pte_low; 33 } 34 35 #define pmd_read_atomic pmd_read_atomic 36 /* 37 * pte_offset_map_lock on 32bit PAE kernels was reading the pmd_t with 38 * a "*pmdp" dereference done by gcc. Problem is, in certain places 39 * where pte_offset_map_lock is called, concurrent page faults are 40 * allowed, if the mmap_sem is hold for reading. An example is mincore 41 * vs page faults vs MADV_DONTNEED. On the page fault side 42 * pmd_populate rightfully does a set_64bit, but if we're reading the 43 * pmd_t with a "*pmdp" on the mincore side, a SMP race can happen 44 * because gcc will not read the 64bit of the pmd atomically. To fix 45 * this all places running pmd_offset_map_lock() while holding the 46 * mmap_sem in read mode, shall read the pmdp pointer using this 47 * function to know if the pmd is null nor not, and in turn to know if 48 * they can run pmd_offset_map_lock or pmd_trans_huge or other pmd 49 * operations. 50 * 51 * Without THP if the mmap_sem is hold for reading, the pmd can only 52 * transition from null to not null while pmd_read_atomic runs. So 53 * we can always return atomic pmd values with this function. 54 * 55 * With THP if the mmap_sem is hold for reading, the pmd can become 56 * trans_huge or none or point to a pte (and in turn become "stable") 57 * at any time under pmd_read_atomic. We could read it really 58 * atomically here with a atomic64_read for the THP enabled case (and 59 * it would be a whole lot simpler), but to avoid using cmpxchg8b we 60 * only return an atomic pmdval if the low part of the pmdval is later 61 * found stable (i.e. pointing to a pte). And we're returning a none 62 * pmdval if the low part of the pmd is none. In some cases the high 63 * and low part of the pmdval returned may not be consistent if THP is 64 * enabled (the low part may point to previously mapped hugepage, 65 * while the high part may point to a more recently mapped hugepage), 66 * but pmd_none_or_trans_huge_or_clear_bad() only needs the low part 67 * of the pmd to be read atomically to decide if the pmd is unstable 68 * or not, with the only exception of when the low part of the pmd is 69 * zero in which case we return a none pmd. 70 */ 71 static inline pmd_t pmd_read_atomic(pmd_t *pmdp) 72 { 73 pmdval_t ret; 74 u32 *tmp = (u32 *)pmdp; 75 76 ret = (pmdval_t) (*tmp); 77 if (ret) { 78 /* 79 * If the low part is null, we must not read the high part 80 * or we can end up with a partial pmd. 81 */ 82 smp_rmb(); 83 ret |= ((pmdval_t)*(tmp + 1)) << 32; 84 } 85 86 return (pmd_t) { ret }; 87 } 88 89 static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte) 90 { 91 set_64bit((unsigned long long *)(ptep), native_pte_val(pte)); 92 } 93 94 static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd) 95 { 96 set_64bit((unsigned long long *)(pmdp), native_pmd_val(pmd)); 97 } 98 99 static inline void native_set_pud(pud_t *pudp, pud_t pud) 100 { 101 set_64bit((unsigned long long *)(pudp), native_pud_val(pud)); 102 } 103 104 /* 105 * For PTEs and PDEs, we must clear the P-bit first when clearing a page table 106 * entry, so clear the bottom half first and enforce ordering with a compiler 107 * barrier. 108 */ 109 static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr, 110 pte_t *ptep) 111 { 112 ptep->pte_low = 0; 113 smp_wmb(); 114 ptep->pte_high = 0; 115 } 116 117 static inline void native_pmd_clear(pmd_t *pmd) 118 { 119 u32 *tmp = (u32 *)pmd; 120 *tmp = 0; 121 smp_wmb(); 122 *(tmp + 1) = 0; 123 } 124 125 static inline void native_pud_clear(pud_t *pudp) 126 { 127 } 128 129 static inline void pud_clear(pud_t *pudp) 130 { 131 set_pud(pudp, __pud(0)); 132 133 /* 134 * According to Intel App note "TLBs, Paging-Structure Caches, 135 * and Their Invalidation", April 2007, document 317080-001, 136 * section 8.1: in PAE mode we explicitly have to flush the 137 * TLB via cr3 if the top-level pgd is changed... 138 * 139 * Currently all places where pud_clear() is called either have 140 * flush_tlb_mm() followed or don't need TLB flush (x86_64 code or 141 * pud_clear_bad()), so we don't need TLB flush here. 142 */ 143 } 144 145 #ifdef CONFIG_SMP 146 static inline pte_t native_ptep_get_and_clear(pte_t *ptep) 147 { 148 pte_t res; 149 150 /* xchg acts as a barrier before the setting of the high bits */ 151 res.pte_low = xchg(&ptep->pte_low, 0); 152 res.pte_high = ptep->pte_high; 153 ptep->pte_high = 0; 154 155 return res; 156 } 157 #else 158 #define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp) 159 #endif 160 161 #ifdef CONFIG_SMP 162 union split_pmd { 163 struct { 164 u32 pmd_low; 165 u32 pmd_high; 166 }; 167 pmd_t pmd; 168 }; 169 static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp) 170 { 171 union split_pmd res, *orig = (union split_pmd *)pmdp; 172 173 /* xchg acts as a barrier before setting of the high bits */ 174 res.pmd_low = xchg(&orig->pmd_low, 0); 175 res.pmd_high = orig->pmd_high; 176 orig->pmd_high = 0; 177 178 return res.pmd; 179 } 180 #else 181 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp) 182 #endif 183 184 #ifdef CONFIG_SMP 185 union split_pud { 186 struct { 187 u32 pud_low; 188 u32 pud_high; 189 }; 190 pud_t pud; 191 }; 192 193 static inline pud_t native_pudp_get_and_clear(pud_t *pudp) 194 { 195 union split_pud res, *orig = (union split_pud *)pudp; 196 197 /* xchg acts as a barrier before setting of the high bits */ 198 res.pud_low = xchg(&orig->pud_low, 0); 199 res.pud_high = orig->pud_high; 200 orig->pud_high = 0; 201 202 return res.pud; 203 } 204 #else 205 #define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp) 206 #endif 207 208 /* Encode and de-code a swap entry */ 209 #define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > 5) 210 #define __swp_type(x) (((x).val) & 0x1f) 211 #define __swp_offset(x) ((x).val >> 5) 212 #define __swp_entry(type, offset) ((swp_entry_t){(type) | (offset) << 5}) 213 #define __pte_to_swp_entry(pte) ((swp_entry_t){ (pte).pte_high }) 214 #define __swp_entry_to_pte(x) ((pte_t){ { .pte_high = (x).val } }) 215 216 #define gup_get_pte gup_get_pte 217 /* 218 * WARNING: only to be used in the get_user_pages_fast() implementation. 219 * 220 * With get_user_pages_fast(), we walk down the pagetables without taking 221 * any locks. For this we would like to load the pointers atomically, 222 * but that is not possible (without expensive cmpxchg8b) on PAE. What 223 * we do have is the guarantee that a PTE will only either go from not 224 * present to present, or present to not present or both -- it will not 225 * switch to a completely different present page without a TLB flush in 226 * between; something that we are blocking by holding interrupts off. 227 * 228 * Setting ptes from not present to present goes: 229 * 230 * ptep->pte_high = h; 231 * smp_wmb(); 232 * ptep->pte_low = l; 233 * 234 * And present to not present goes: 235 * 236 * ptep->pte_low = 0; 237 * smp_wmb(); 238 * ptep->pte_high = 0; 239 * 240 * We must ensure here that the load of pte_low sees 'l' iff pte_high 241 * sees 'h'. We load pte_high *after* loading pte_low, which ensures we 242 * don't see an older value of pte_high. *Then* we recheck pte_low, 243 * which ensures that we haven't picked up a changed pte high. We might 244 * have gotten rubbish values from pte_low and pte_high, but we are 245 * guaranteed that pte_low will not have the present bit set *unless* 246 * it is 'l'. Because get_user_pages_fast() only operates on present ptes 247 * we're safe. 248 */ 249 static inline pte_t gup_get_pte(pte_t *ptep) 250 { 251 pte_t pte; 252 253 do { 254 pte.pte_low = ptep->pte_low; 255 smp_rmb(); 256 pte.pte_high = ptep->pte_high; 257 smp_rmb(); 258 } while (unlikely(pte.pte_low != ptep->pte_low)); 259 260 return pte; 261 } 262 263 #endif /* _ASM_X86_PGTABLE_3LEVEL_H */ 264