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SubjectRe: [RFC V1 02/31] mm/mmap: Clarify protection_map[] indices
The 01/24/2022 18:26, Anshuman Khandual wrote:
> protection_map[] maps vm_flags access combinations into page protection
> value as defined by the platform via __PXXX and __SXXX macros. The array
> indices in protection_map[], represents vm_flags access combinations but
> it's not very intuitive to derive. This makes it clear and explicit.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> mm/mmap.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 1e8fdb0b51ed..254d716220df 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -102,8 +102,22 @@ static void unmap_region(struct mm_struct *mm,
> * x: (yes) yes
> */
> pgprot_t protection_map[16] __ro_after_init = {
> - __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
> - __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
> + [VM_NONE] = __P000,
> + [VM_READ] = __P001,
> + [VM_WRITE] = __P010,
> + [VM_READ|VM_WRITE] = __P011,
> + [VM_EXEC] = __P100,
> + [VM_EXEC|VM_READ] = __P101,
> + [VM_EXEC|VM_WRITE] = __P110,
> + [VM_EXEC|VM_READ|VM_WRITE] = __P111,
> + [VM_SHARED] = __S000,
> + [VM_SHARED|VM_READ] = __S001,
> + [VM_SHARED|VM_WRITE] = __S010,
> + [VM_SHARED|VM_READ|VM_WRITE] = __S011,
> + [VM_SHARED|VM_EXEC] = __S100,
> + [VM_SHARED|VM_READ|VM_EXEC] = __S101,
> + [VM_SHARED|VM_WRITE|VM_EXEC] = __S110,
> + [VM_SHARED|VM_READ|VM_WRITE|VM_EXEC] = __S111

Just a little bit picky:)
Would you mind rearranging vm_flags access commbination in the order as
the access bits appear in __SXXX or __PXXX? For example, change the following:

[VM_SHARED|VM_READ|VM_WRITE|VM_EXEC] = __S111
to
[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = __S111

I think it's would be more clear for looking.

Best,
// Firo

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