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    Subject[tip:mm/pkeys] x86/mm/gup: Simplify get_user_pages() PTE bit handling
    Commit-ID:  1874f6895c92d991ccf85edcc55a0d9dd552d71c
    Gitweb: http://git.kernel.org/tip/1874f6895c92d991ccf85edcc55a0d9dd552d71c
    Author: Dave Hansen <dave.hansen@linux.intel.com>
    AuthorDate: Fri, 12 Feb 2016 13:02:18 -0800
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 18 Feb 2016 09:32:44 +0100

    x86/mm/gup: 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.

    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>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Dave Hansen <dave@sr71.net>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: linux-mm@kvack.org
    Link: http://lkml.kernel.org/r/20160212210218.3A2D4045@viggo.jf.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/mm/gup.c | 38 ++++++++++++++++++++++----------------
    1 file changed, 22 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
    index ce5e454..2f0a329 100644
    --- a/arch/x86/mm/gup.c
    +++ b/arch/x86/mm/gup.c
    @@ -75,6 +75,24 @@ static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
    }

    /*
    + * '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.
    @@ -83,14 +101,9 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
    unsigned long end, int write, struct page **pages, int *nr)
    {
    struct dev_pagemap *pgmap = NULL;
    - unsigned long mask;
    int nr_start = *nr;
    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);
    @@ -110,7 +123,8 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
    pte_unmap(ptep);
    return 0;
    }
    - } else if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
    + } else if (!pte_allows_gup(pte_val(pte), write) ||
    + pte_special(pte)) {
    pte_unmap(ptep);
    return 0;
    }
    @@ -164,14 +178,10 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
    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;

    VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
    @@ -231,14 +241,10 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
    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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