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.
We need to use the bits for our _PAGE_PRESENT check since
pte_present() is also true for _PAGE_PROTNONE, and we have no
accessor for _PAGE_USER, so need it there as well.
But we might as well just use pte_write() since we have it and
let the compiler work its magic on optimizing it.
This also consolidates the three identical copies of this code.
---
b/arch/x86/mm/gup.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
diff -puN arch/x86/mm/gup.c~pkeys-16-gup-swizzle arch/x86/mm/gup.c
--- a/arch/x86/mm/gup.c~pkeys-16-gup-swizzle 2015-09-16 10:48:17.002226145
-0700
+++ b/arch/x86/mm/gup.c 2015-09-16 10:48:17.006226326 -0700
@@ -63,6 +63,19 @@ retry:
#endif
}
+static inline int pte_allows_gup(pte_t pte, int write)
+{
+ /*
+ * Note that pte_present() is true for !_PAGE_PRESENT
+ * but _PAGE_PROTNONE, so we can not use it here.
+ */
+ if (!(pte_flags(pte) & (_PAGE_PRESENT|_PAGE_USER)))
+ return 0;
+ if (write && !pte_write(pte))
+ 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
@@ -71,13 +84,8 @@ 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 +96,8 @@ 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, write) ||
+ pte_special(pte)) {
pte_unmap(ptep);
return 0;
}
@@ -117,15 +125,11 @@ 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;
pte_t pte = *(pte_t *)&pmd;
struct page *head, *page;
int refs;
- mask = _PAGE_PRESENT|_PAGE_USER;
- if (write)
- mask |= _PAGE_RW;
- if ((pte_flags(pte) & mask) != mask)
+ if (!pte_allows_gup(pte, write))
return 0;
/* hugepages are never "special" */
VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
@@ -194,15 +198,11 @@ 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;
pte_t pte = *(pte_t *)&pud;
struct page *head, *page;
int refs;
- mask = _PAGE_PRESENT|_PAGE_USER;
- if (write)
- mask |= _PAGE_RW;
- if ((pte_flags(pte) & mask) != mask)
+ if (!pte_allows_gup(pte, write))
return 0;
/* hugepages are never "special" */
VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
_
--
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