diff options
| -rw-r--r-- | include/linux/pgtable.h | 55 | ||||
| -rw-r--r-- | mm/gup.c | 58 |
2 files changed, 56 insertions, 57 deletions
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 71125a4676c4..ed9266cc115b 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -258,6 +258,61 @@ static inline pte_t ptep_get(pte_t *ptep) } #endif +#ifdef CONFIG_GUP_GET_PTE_LOW_HIGH +/* + * WARNING: only to be used in the get_user_pages_fast() implementation. + * + * With get_user_pages_fast(), we walk down the pagetables without taking any + * locks. For this we would like to load the pointers atomically, but sometimes + * that is not possible (e.g. without expensive cmpxchg8b on x86_32 PAE). What + * we do have is the guarantee that a PTE will only either go from not present + * to present, or present to not present or both -- it will not switch to a + * completely different present page without a TLB flush in between; something + * that we are blocking by holding interrupts off. + * + * Setting ptes from not present to present goes: + * + * ptep->pte_high = h; + * smp_wmb(); + * ptep->pte_low = l; + * + * And present to not present goes: + * + * ptep->pte_low = 0; + * smp_wmb(); + * ptep->pte_high = 0; + * + * We must ensure here that the load of pte_low sees 'l' IFF pte_high sees 'h'. + * We load pte_high *after* loading pte_low, which ensures we don't see an older + * value of pte_high. *Then* we recheck pte_low, which ensures that we haven't + * picked up a changed pte high. We might have gotten rubbish values from + * pte_low and pte_high, but we are guaranteed that pte_low will not have the + * present bit set *unless* it is 'l'. Because get_user_pages_fast() only + * operates on present ptes we're safe. + */ +static inline pte_t ptep_get_lockless(pte_t *ptep) +{ + pte_t pte; + + do { + pte.pte_low = ptep->pte_low; + smp_rmb(); + pte.pte_high = ptep->pte_high; + smp_rmb(); + } while (unlikely(pte.pte_low != ptep->pte_low)); + + return pte; +} +#else /* CONFIG_GUP_GET_PTE_LOW_HIGH */ +/* + * We require that the PTE can be read atomically. + */ +static inline pte_t ptep_get_lockless(pte_t *ptep) +{ + return ptep_get(ptep); +} +#endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */ + #ifdef CONFIG_TRANSPARENT_HUGEPAGE #ifndef __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm, @@ -2085,62 +2085,6 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags) put_page(page); } -#ifdef CONFIG_GUP_GET_PTE_LOW_HIGH - -/* - * WARNING: only to be used in the get_user_pages_fast() implementation. - * - * With get_user_pages_fast(), we walk down the pagetables without taking any - * locks. For this we would like to load the pointers atomically, but sometimes - * that is not possible (e.g. without expensive cmpxchg8b on x86_32 PAE). What - * we do have is the guarantee that a PTE will only either go from not present - * to present, or present to not present or both -- it will not switch to a - * completely different present page without a TLB flush in between; something - * that we are blocking by holding interrupts off. - * - * Setting ptes from not present to present goes: - * - * ptep->pte_high = h; - * smp_wmb(); - * ptep->pte_low = l; - * - * And present to not present goes: - * - * ptep->pte_low = 0; - * smp_wmb(); - * ptep->pte_high = 0; - * - * We must ensure here that the load of pte_low sees 'l' IFF pte_high sees 'h'. - * We load pte_high *after* loading pte_low, which ensures we don't see an older - * value of pte_high. *Then* we recheck pte_low, which ensures that we haven't - * picked up a changed pte high. We might have gotten rubbish values from - * pte_low and pte_high, but we are guaranteed that pte_low will not have the - * present bit set *unless* it is 'l'. Because get_user_pages_fast() only - * operates on present ptes we're safe. - */ -static inline pte_t gup_get_pte(pte_t *ptep) -{ - pte_t pte; - - do { - pte.pte_low = ptep->pte_low; - smp_rmb(); - pte.pte_high = ptep->pte_high; - smp_rmb(); - } while (unlikely(pte.pte_low != ptep->pte_low)); - - return pte; -} -#else /* CONFIG_GUP_GET_PTE_LOW_HIGH */ -/* - * We require that the PTE can be read atomically. - */ -static inline pte_t gup_get_pte(pte_t *ptep) -{ - return ptep_get(ptep); -} -#endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */ - static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start, unsigned int flags, struct page **pages) @@ -2166,7 +2110,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, ptem = ptep = pte_offset_map(&pmd, addr); do { - pte_t pte = gup_get_pte(ptep); + pte_t pte = ptep_get_lockless(ptep); struct page *head, *page; /* |