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[PATCH 16/32] x86, mm: simplify get_user_pages() PTE bit handling

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  [PATCH 16/32] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen <dave@sr71.net> - 2015-12-14 20:10 +0100
    Re: [PATCH 16/32] x86, mm: simplify get_user_pages() PTE bit  handling Thomas Gleixner <tglx@linutronix.de> - 2015-12-14 21:00 +0100

#1291460 — [PATCH 16/32] x86, mm: simplify get_user_pages() PTE bit handling

From: Dave Hansen <dave.hansen@linux.intel.com>

The current get_user_pages() code is a wee bit more complicated
than it needs to be for pte bit checking.  Currently, it establishes
a mask of required pte _PAGE_* bits and ensures that the pte it
goes after has all those bits.

This consolidates the three identical copies of this code.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

 b/arch/x86/mm/gup.c |   39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff -puN arch/x86/mm/gup.c~pkeys-12-gup-swizzle arch/x86/mm/gup.c
--- a/arch/x86/mm/gup.c~pkeys-12-gup-swizzle	2015-12-14 10:42:45.691932481 -0800
+++ b/arch/x86/mm/gup.c	2015-12-14 10:42:45.694932616 -0800
@@ -64,6 +64,24 @@ retry:
 }
 
 /*
+ * 'pteval' can come from a pte, pmd or pud.  We only check
+ * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
+ * same value on all 3 types.
+ */
+static inline int pte_allows_gup(unsigned long pteval, int write)
+{
+	unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
+
+	if (write)
+		need_pte_bits |= _PAGE_RW;
+
+	if ((pteval & need_pte_bits) != need_pte_bits)
+		return 0;
+
+	return 1;
+}
+
+/*
  * The performance critical leaf functions are made noinline otherwise gcc
  * inlines everything into a single function which results in too much
  * register pressure.
@@ -71,13 +89,8 @@ retry:
 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 		unsigned long end, int write, struct page **pages, int *nr)
 {
-	unsigned long mask;
 	pte_t *ptep;
 
-	mask = _PAGE_PRESENT|_PAGE_USER;
-	if (write)
-		mask |= _PAGE_RW;
-
 	ptep = pte_offset_map(&pmd, addr);
 	do {
 		pte_t pte = gup_get_pte(ptep);
@@ -88,8 +101,8 @@ static noinline int gup_pte_range(pmd_t
 			pte_unmap(ptep);
 			return 0;
 		}
-
-		if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
+		if (!pte_allows_gup(pte_val(pte), write) ||
+		    pte_special(pte)) {
 			pte_unmap(ptep);
 			return 0;
 		}
@@ -117,14 +130,10 @@ static inline void get_head_page_multipl
 static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
 		unsigned long end, int write, struct page **pages, int *nr)
 {
-	unsigned long mask;
 	struct page *head, *page;
 	int refs;
 
-	mask = _PAGE_PRESENT|_PAGE_USER;
-	if (write)
-		mask |= _PAGE_RW;
-	if ((pmd_flags(pmd) & mask) != mask)
+	if (!pte_allows_gup(pmd_val(pmd), write))
 		return 0;
 	/* hugepages are never "special" */
 	VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL);
@@ -193,14 +202,10 @@ static int gup_pmd_range(pud_t pud, unsi
 static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
 		unsigned long end, int write, struct page **pages, int *nr)
 {
-	unsigned long mask;
 	struct page *head, *page;
 	int refs;
 
-	mask = _PAGE_PRESENT|_PAGE_USER;
-	if (write)
-		mask |= _PAGE_RW;
-	if ((pud_flags(pud) & mask) != mask)
+	if (!pte_allows_gup(pud_val(pud), write))
 		return 0;
 	/* hugepages are never "special" */
 	VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);
_
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#1291515 — Re: [PATCH 16/32] x86, mm: simplify get_user_pages() PTE bit handling

On Mon, 14 Dec 2015, Dave Hansen wrote:
> The current get_user_pages() code is a wee bit more complicated
> than it needs to be for pte bit checking.  Currently, it establishes
> a mask of required pte _PAGE_* bits and ensures that the pte it
> goes after has all those bits.
> 
> This consolidates the three identical copies of this code.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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