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authorPeter Zijlstra <peterz@infradead.org>2020-11-13 11:41:40 +0100
committerPeter Zijlstra <peterz@infradead.org>2020-12-03 10:14:50 +0100
commit2a4a06da8a4b93dd189171eed7a99fffd38f42f3 (patch)
tree953d240c76d33d8b826a74ba1807d0150ca6a5c4 /mm/gup.c
parent20c7775aecea04d8ca322039969d49dcf568e0e9 (diff)
mm/gup: Provide gup_get_pte() more generic
In order to write another lockless page-table walker, we need gup_get_pte() exposed. While doing that, rename it to ptep_get_lockless() to match the existing ptep_get() naming. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20201126121121.036370527@infradead.org
Diffstat (limited to 'mm/gup.c')
-rw-r--r--mm/gup.c58
1 files changed, 1 insertions, 57 deletions
diff --git a/mm/gup.c b/mm/gup.c
index 98eb8e6d2609..44b0c6b89602 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -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;
/*