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Subject[PATCH 3/7] mm/gup: Move page table entry dereference into helper
Date
This is preparation patch for transition of x86 to generic GUP_fast()
implementation.

On x86 PAE, page table entry is larger than sizeof(long) and we would
need to provide helper that can read the entry atomically.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/gup.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index a62a778ce4ec..ed2259dc4606 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1189,6 +1189,17 @@ struct page *get_dump_page(unsigned long addr)
*/
#ifdef CONFIG_HAVE_GENERIC_RCU_GUP

+#ifndef gup_get_pte
+/*
+ * We assume that the pte can be read atomically. If this is not the case for
+ * your architecture, please provide the helper.
+ */
+static inline pte_t gup_get_pte(pte_t *ptep)
+{
+ return READ_ONCE(*ptep);
+}
+#endif
+
#ifdef __HAVE_ARCH_PTE_SPECIAL
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
int write, struct page **pages, int *nr)
@@ -1198,14 +1209,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

ptem = ptep = pte_offset_map(&pmd, addr);
do {
- /*
- * In the line below we are assuming that the pte can be read
- * atomically. If this is not the case for your architecture,
- * please wrap this in a helper function!
- *
- * for an example see gup_get_pte in arch/x86/mm/gup.c
- */
- pte_t pte = READ_ONCE(*ptep);
+ pte_t pte = gup_get_pte(ptep);
struct page *head, *page;

/*
--
2.11.0
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