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    Subject[tip:x86/mm] x86/kasan: Prepare clear_pgds() to switch to <asm-generic/pgtable-nop4d.h>
    Commit-ID:  d691a3cf8004784303f0a4c1c036edfaa7d64d0b
    Gitweb: http://git.kernel.org/tip/d691a3cf8004784303f0a4c1c036edfaa7d64d0b
    Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    AuthorDate: Fri, 17 Mar 2017 21:55:13 +0300
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 27 Mar 2017 08:56:41 +0200

    x86/kasan: Prepare clear_pgds() to switch to <asm-generic/pgtable-nop4d.h>

    With folded p4d, pgd_clear() is a nop. Change clear_pgds() to use
    p4d_clear() instead.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Acked-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: linux-arch@vger.kernel.org
    Cc: linux-mm@kvack.org
    Link: http://lkml.kernel.org/r/20170317185515.8636-5-kirill.shutemov@linux.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/mm/kasan_init_64.c | 15 +++++++++++++--
    1 file changed, 13 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
    index 8d63d7a..7b81f01 100644
    --- a/arch/x86/mm/kasan_init_64.c
    +++ b/arch/x86/mm/kasan_init_64.c
    @@ -32,8 +32,19 @@ static int __init map_range(struct range *range)
    static void __init clear_pgds(unsigned long start,
    unsigned long end)
    {
    - for (; start < end; start += PGDIR_SIZE)
    - pgd_clear(pgd_offset_k(start));
    + pgd_t *pgd;
    +
    + for (; start < end; start += PGDIR_SIZE) {
    + pgd = pgd_offset_k(start);
    + /*
    + * With folded p4d, pgd_clear() is nop, use p4d_clear()
    + * instead.
    + */
    + if (CONFIG_PGTABLE_LEVELS < 5)
    + p4d_clear(p4d_offset(pgd, start));
    + else
    + pgd_clear(pgd);
    + }
    }

    static void __init kasan_map_early_shadow(pgd_t *pgd)
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