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Groups > linux.kernel > #1602536

[PATCH 3/7] mm/gup: Move page table entry dereference into helper

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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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[PATCH 0/7] Switch x86 to generic get_user_pages_fast() implementation "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 16:30 +0100
  [PATCH 3/7] mm/gup: Move page table entry dereference into helper "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 16:30 +0100
    [tip:x86/mm] mm/gup: Move page table entry dereference into helper  function "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com> - 2017-03-18 11:00 +0100
  [PATCH 4/7] mm/gup: Make pages referenced during generic get_user_pages_fast() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 16:30 +0100
    [tip:x86/mm] mm/gup: Mark all pages PageReferenced in generic  get_user_pages_fast() "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com> - 2017-03-18 11:00 +0100
  [PATCH 7/7] x86/mm: Switch to generic get_user_page_fast() implementation "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 16:30 +0100
    Re: [PATCH 7/7] x86/mm: Switch to generic get_user_page_fast()  implementation Peter Zijlstra <peterz@infradead.org> - 2017-03-16 18:30 +0100
      Re: [PATCH 7/7] x86/mm: Switch to generic get_user_page_fast()  implementation "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-03-16 20:20 +0100
    [PATCHv2 7/7] x86/mm: Switch to generic get_user_page_fast() implementation "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 22:40 +0100
      Re: [PATCHv2 7/7] x86/mm: Switch to generic get_user_page_fast()  implementation "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-17 18:40 +0100
      [tip:x86/mm] x86/mm/gup: Switch GUP to the generic  get_user_page_fast() implementation "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com> - 2017-03-18 12:50 +0100
  [PATCH 1/7] mm: Drop arch_pte_access_permitted() mmu hook "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-16 16:40 +0100
    [tip:x86/mm] mm/gup: Drop the arch_pte_access_permitted() MMU  callback "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com> - 2017-03-18 11:00 +0100
  Re: [PATCH 0/7] Switch x86 to generic get_user_pages_fast() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-16 19:10 +0100
  Re: [PATCH 0/7] Switch x86 to generic get_user_pages_fast()  implementation Ingo Molnar <mingo@kernel.org> - 2017-03-17 09:40 +0100

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