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    Subject[PATCH 06/12] x86, pkeys: store protection in high VMA flags
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    vma->vm_flags is an 'unsigned long', so has space for 32 flags
    on 32-bit architectures. The high 32 bits are unused on 64-bit
    platforms. We've steered away from using the unused high VMA
    bits for things because we would have difficulty supporting it
    on 32-bit.

    Protection Keys are not available in 32-bit mode, so there is
    no concern about supporting this feature in 32-bit mode or on
    32-bit CPUs.

    This patch carves out 4 bits from the high half of
    vma->vm_flags and allows architectures to set config option
    to make them available.

    ---

    b/arch/x86/Kconfig | 1 +
    b/include/linux/mm.h | 7 +++++++
    b/mm/Kconfig | 3 +++
    3 files changed, 11 insertions(+)

    diff -puN arch/x86/Kconfig~pkeys-7-eat-high-vma-flags arch/x86/Kconfig
    --- a/arch/x86/Kconfig~pkeys-7-eat-high-vma-flags 2015-05-07 10:31:42.943257595 -0700
    +++ b/arch/x86/Kconfig 2015-05-07 10:31:42.951257956 -0700
    @@ -142,6 +142,7 @@ config X86
    select ACPI_LEGACY_TABLES_LOOKUP if ACPI
    select X86_FEATURE_NAMES if PROC_FS
    select SRCU
    + select ARCH_USES_HIGH_VMA_FLAGS if X86_64

    config INSTRUCTION_DECODER
    def_bool y
    diff -puN include/linux/mm.h~pkeys-7-eat-high-vma-flags include/linux/mm.h
    --- a/include/linux/mm.h~pkeys-7-eat-high-vma-flags 2015-05-07 10:31:42.945257685 -0700
    +++ b/include/linux/mm.h 2015-05-07 10:31:42.951257956 -0700
    @@ -153,6 +153,13 @@ extern unsigned int kobjsize(const void
    #define VM_NOHUGEPAGE 0x40000000 /* MADV_NOHUGEPAGE marked this vma */
    #define VM_MERGEABLE 0x80000000 /* KSM may merge identical pages */

    +#ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
    +#define VM_HIGH_ARCH_1 0x100000000 /* bit only usable on 64-bit architectures */
    +#define VM_HIGH_ARCH_2 0x200000000 /* bit only usable on 64-bit architectures */
    +#define VM_HIGH_ARCH_3 0x400000000 /* bit only usable on 64-bit architectures */
    +#define VM_HIGH_ARCH_4 0x800000000 /* bit only usable on 64-bit architectures */
    +#endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
    +
    #if defined(CONFIG_X86)
    # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */
    #elif defined(CONFIG_PPC)
    diff -puN mm/Kconfig~pkeys-7-eat-high-vma-flags mm/Kconfig
    --- a/mm/Kconfig~pkeys-7-eat-high-vma-flags 2015-05-07 10:31:42.947257775 -0700
    +++ b/mm/Kconfig 2015-05-07 10:31:42.952258001 -0700
    @@ -635,3 +635,6 @@ config MAX_STACK_SIZE_MB
    changed to a smaller value in which case that is used.

    A sane initial value is 80 MB.
    +
    +config ARCH_USES_HIGH_VMA_FLAGS
    + bool
    _

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