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SubjectRe: [RFC V1 31/31] mm/mmap: Define macros for vm_flags access permission combinations
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On 1/24/22 6:27 PM, Anshuman Khandual wrote:
> These macros will be useful in cleaning up the all those switch statements
> in vm_get_page_prot() across all platforms.
>
> 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>
> ---
> include/linux/mm.h | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6c0844b99b3e..b3691eeec500 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2828,6 +2828,45 @@ static inline bool range_in_vma(struct vm_area_struct *vma,
> return (vma && vma->vm_start <= start && end <= vma->vm_end);
> }
>
> +/*
> + * Access permission related vm_flags combination is used to map into
> + * platform defined page protection flags. This enumeration helps in
> + * abstracting out possible indices after vm_flags is probed for all
> + * access permission i.e (VM_SHARED | VM_EXEC | VM_READ | VM_WRITE).
> + *
> + * VM_EXEC ---------------------|
> + * |
> + * VM_WRITE ---------------| |
> + * | |
> + * VM_READ -----------| | |
> + * | | |
> + * VM_SHARED ----| | | |
> + * | | | |
> + * v v v v
> + * VMFLAGS_IDX_(S|X)(R|X)(W|X)(E|X)
> + *
> + * X - Indicates that the access flag is absent
> + */
> +enum vmflags_idx {
> + VMFLAGS_IDX_XXXX, /* (VM_NONE) */
> + VMFLAGS_IDX_XRXX, /* (VM_READ) */
> + VMFLAGS_IDX_XXWX, /* (VM_WRITE) */
> + VMFLAGS_IDX_XRWX, /* (VM_READ | VM_WRITE) */
> + VMFLAGS_IDX_XXXE, /* (VM_EXEC) */
> + VMFLAGS_IDX_XRXE, /* (VM_EXEC | VM_READ) */
> + VMFLAGS_IDX_XXWE, /* (VM_EXEC | VM_WRITE) */
> + VMFLAGS_IDX_XRWE, /* (VM_EXEC | VM_READ | VM_WRITE) */
> + VMFLAGS_IDX_SXXX, /* (VM_SHARED | VM_NONE) */
> + VMFLAGS_IDX_SRXX, /* (VM_SHARED | VM_READ) */
> + VMFLAGS_IDX_SXWX, /* (VM_SHARED | VM_WRITE) */
> + VMFLAGS_IDX_SRWX, /* (VM_SHARED | VM_READ | VM_WRITE) */
> + VMFLAGS_IDX_SXXE, /* (VM_SHARED | VM_EXEC) */
> + VMFLAGS_IDX_SRXE, /* (VM_SHARED | VM_EXEC | VM_READ) */
> + VMFLAGS_IDX_SXWE, /* (VM_SHARED | VM_EXEC | VM_WRITE) */
> + VMFLAGS_IDX_SRWE, /* (VM_SHARED | VM_EXEC | VM_READ | VM_WRITE) */
> + VMFLAGS_IDX_MAX
> +};

Defining platform specific vm_get_page_prot() involves a switch statement
with various vm_flags access combinations as cases. Hence I am wondering,
will it help to use these above macros, instead of existing combinations
separated with '|' flags. I can move this patch earlier in the series and
change all platform switch cases. Please do suggest. Thank you.

- Anshuman

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