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    Subject[PATCH v4 14/39] mm: Move VM_UFFD_MINOR_BIT from 37 to 38
    Date
    From: Yu-cheng Yu <yu-cheng.yu@intel.com>

    The x86 Control-flow Enforcement Technology (CET) feature includes a new
    type of memory called shadow stack. This shadow stack memory has some
    unusual properties, which requires some core mm changes to function
    properly.

    Future patches will introduce a new VM flag VM_SHADOW_STACK that will be
    VM_HIGH_ARCH_BIT_5. VM_HIGH_ARCH_BIT_1 through VM_HIGH_ARCH_BIT_4 are
    bits 32-36, and bit 37 is the unrelated VM_UFFD_MINOR_BIT. For the sake
    of order, make all VM_HIGH_ARCH_BITs stay together by moving
    VM_UFFD_MINOR_BIT from 37 to 38. This will allow VM_SHADOW_STACK to be
    introduced as 37.

    Tested-by: Pengfei Xu <pengfei.xu@intel.com>
    Tested-by: John Allen <john.allen@amd.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Acked-by: Peter Xu <peterx@redhat.com>
    Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
    Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
    Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    Cc: Peter Xu <peterx@redhat.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    ---
    include/linux/mm.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index bfac5a166cb8..9ae6bc38d0b7 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -354,7 +354,7 @@ extern unsigned int kobjsize(const void *objp);
    #endif

    #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
    -# define VM_UFFD_MINOR_BIT 37
    +# define VM_UFFD_MINOR_BIT 38
    # define VM_UFFD_MINOR BIT(VM_UFFD_MINOR_BIT) /* UFFD minor faults */
    #else /* !CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
    # define VM_UFFD_MINOR VM_NONE
    --
    2.17.1
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