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Date: Wed, 16 Sep 2015 10:49:07 -0700 From: Dave Hansen <dave@...1.net> To: dave@...1.net Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: [PATCH 13/26] mm: simplify get_user_pages() PTE bit handling 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); _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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