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1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_X86_PGTABLE_3LEVEL_H
3 #define _ASM_X86_PGTABLE_3LEVEL_H
5 /*
6 * Intel Physical Address Extension (PAE) Mode - three-level page
7 * tables on PPro+ CPUs.
9 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
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))
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
28 static inline void native_set_pte(pte_t *ptep, pte_t pte)
30 ptep->pte_high = pte.pte_high;
31 smp_wmb();
32 ptep->pte_low = pte.pte_low;
35 #define pmd_read_atomic pmd_read_atomic
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.
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.
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.
71 static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
73 pmdval_t ret;
74 u32 *tmp = (u32 *)pmdp;
76 ret = (pmdval_t) (*tmp);
77 if (ret) {
79 * If the low part is null, we must not read the high part
80 * or we can end up with a partial pmd.
82 smp_rmb();
83 ret |= ((pmdval_t)*(tmp + 1)) << 32;
86 return (pmd_t) { ret };
89 static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
91 set_64bit((unsigned long long *)(ptep), native_pte_val(pte));
94 static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
96 set_64bit((unsigned long long *)(pmdp), native_pmd_val(pmd));
99 static inline void native_set_pud(pud_t *pudp, pud_t pud)
101 set_64bit((unsigned long long *)(pudp), native_pud_val(pud));
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.
109 static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr,
110 pte_t *ptep)
112 ptep->pte_low = 0;
113 smp_wmb();
114 ptep->pte_high = 0;
117 static inline void native_pmd_clear(pmd_t *pmd)
119 u32 *tmp = (u32 *)pmd;
120 *tmp = 0;
121 smp_wmb();
122 *(tmp + 1) = 0;
125 static inline void native_pud_clear(pud_t *pudp)
129 static inline void pud_clear(pud_t *pudp)
131 set_pud(pudp, __pud(0));
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...
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.
145 #ifdef CONFIG_SMP
146 static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
148 pte_t res;
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;
155 return res;
157 #else
158 #define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
159 #endif
161 union split_pmd {
162 struct {
163 u32 pmd_low;
164 u32 pmd_high;
166 pmd_t pmd;
169 #ifdef CONFIG_SMP
170 static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp)
172 union split_pmd res, *orig = (union split_pmd *)pmdp;
174 /* xchg acts as a barrier before setting of the high bits */
175 res.pmd_low = xchg(&orig->pmd_low, 0);
176 res.pmd_high = orig->pmd_high;
177 orig->pmd_high = 0;
179 return res.pmd;
181 #else
182 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
183 #endif
185 #ifndef pmdp_establish
186 #define pmdp_establish pmdp_establish
187 static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
188 unsigned long address, pmd_t *pmdp, pmd_t pmd)
190 pmd_t old;
193 * If pmd has present bit cleared we can get away without expensive
194 * cmpxchg64: we can update pmdp half-by-half without racing with
195 * anybody.
197 if (!(pmd_val(pmd) & _PAGE_PRESENT)) {
198 union split_pmd old, new, *ptr;
200 ptr = (union split_pmd *)pmdp;
202 new.pmd = pmd;
204 /* xchg acts as a barrier before setting of the high bits */
205 old.pmd_low = xchg(&ptr->pmd_low, new.pmd_low);
206 old.pmd_high = ptr->pmd_high;
207 ptr->pmd_high = new.pmd_high;
208 return old.pmd;
211 do {
212 old = *pmdp;
213 } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd);
215 return old;
217 #endif
219 #ifdef CONFIG_SMP
220 union split_pud {
221 struct {
222 u32 pud_low;
223 u32 pud_high;
225 pud_t pud;
228 static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
230 union split_pud res, *orig = (union split_pud *)pudp;
232 /* xchg acts as a barrier before setting of the high bits */
233 res.pud_low = xchg(&orig->pud_low, 0);
234 res.pud_high = orig->pud_high;
235 orig->pud_high = 0;
237 return res.pud;
239 #else
240 #define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp)
241 #endif
243 /* Encode and de-code a swap entry */
244 #define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > 5)
245 #define __swp_type(x) (((x).val) & 0x1f)
246 #define __swp_offset(x) ((x).val >> 5)
247 #define __swp_entry(type, offset) ((swp_entry_t){(type) | (offset) << 5})
248 #define __pte_to_swp_entry(pte) ((swp_entry_t){ (pte).pte_high })
249 #define __swp_entry_to_pte(x) ((pte_t){ { .pte_high = (x).val } })
251 #define gup_get_pte gup_get_pte
253 * WARNING: only to be used in the get_user_pages_fast() implementation.
255 * With get_user_pages_fast(), we walk down the pagetables without taking
256 * any locks. For this we would like to load the pointers atomically,
257 * but that is not possible (without expensive cmpxchg8b) on PAE. What
258 * we do have is the guarantee that a PTE will only either go from not
259 * present to present, or present to not present or both -- it will not
260 * switch to a completely different present page without a TLB flush in
261 * between; something that we are blocking by holding interrupts off.
263 * Setting ptes from not present to present goes:
265 * ptep->pte_high = h;
266 * smp_wmb();
267 * ptep->pte_low = l;
269 * And present to not present goes:
271 * ptep->pte_low = 0;
272 * smp_wmb();
273 * ptep->pte_high = 0;
275 * We must ensure here that the load of pte_low sees 'l' iff pte_high
276 * sees 'h'. We load pte_high *after* loading pte_low, which ensures we
277 * don't see an older value of pte_high. *Then* we recheck pte_low,
278 * which ensures that we haven't picked up a changed pte high. We might
279 * have gotten rubbish values from pte_low and pte_high, but we are
280 * guaranteed that pte_low will not have the present bit set *unless*
281 * it is 'l'. Because get_user_pages_fast() only operates on present ptes
282 * we're safe.
284 static inline pte_t gup_get_pte(pte_t *ptep)
286 pte_t pte;
288 do {
289 pte.pte_low = ptep->pte_low;
290 smp_rmb();
291 pte.pte_high = ptep->pte_high;
292 smp_rmb();
293 } while (unlikely(pte.pte_low != ptep->pte_low));
295 return pte;
298 #endif /* _ASM_X86_PGTABLE_3LEVEL_H */