linux-kernel - Re: [RFC V1 02/31] mm/mmap: Clarify protection

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Date:   Sat, 5 Feb 2022 17:10:48 +0800
From:   Firo Yang <firogm@...il.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        hch@...radead.org, akpm@...ux-foundation.org
Subject: Re: [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@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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