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

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Message-Id: <20170316152655.37789-4-kirill.shutemov@linux.intel.com>
Date:   Thu, 16 Mar 2017 18:26:51 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Steve Capper <steve.capper@...aro.org>,
        Dann Frazier <dann.frazier@...onical.com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 3/7] mm/gup: Move page table entry dereference into helper

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@...ux.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