Re: [PATCH V4 0/7] mm/mmap: Drop arch_vm_get_page_prot() and arch_filter_pgprot()

Anshuman Khandual
2022-04-08T02:41:21Z

On 4/8/22 04:50, Andrew Morton wrote:
> On Thu, 7 Apr 2022 16:02:44 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>
>> protection_map[] is an array based construct that translates given vm_flags
>> combination. This array contains page protection map, which is populated by
>> the platform via [__S000 .. __S111] and [__P000 .. __P111] exported macros.
>> Primary usage for protection_map[] is for vm_get_page_prot(), which is used
>> to determine page protection value for a given vm_flags. vm_get_page_prot()
>> implementation, could again call platform overrides arch_vm_get_page_prot()
>> and arch_filter_pgprot(). Some platforms override protection_map[] that was
>> originally built with __SXXX/__PXXX with different runtime values.
>>
>> Currently there are multiple layers of abstraction i.e __SXXX/__PXXX macros
>> , protection_map[], arch_vm_get_page_prot() and arch_filter_pgprot() built
>> between the platform and generic MM, finally defining vm_get_page_prot().
>>
>> Hence this series proposes to drop later two abstraction levels and instead
>> just move the responsibility of defining vm_get_page_prot() to the platform
>> (still utilizing generic protection_map[] array) itself making it clean and
>> simple.
>>
>> This first introduces ARCH_HAS_VM_GET_PAGE_PROT which enables the platforms
>> to define custom vm_get_page_prot(). This starts converting platforms that
>> define the overrides arch_filter_pgprot() or arch_vm_get_page_prot() which
>> enables for those constructs to be dropped off completely.
>>
>> The series has been inspired from an earlier discuss with Christoph Hellwig
>>
>> https://lore.kernel.org/all/1632712920-8171-1-git-send-email-anshuman.khandual@arm.com/
>>
>> This series applies on 5.18-rc1 after the following patch.
>>
>> https://lore.kernel.org/all/1643004823-16441-1-git-send-email-anshuman.khandual@arm.com/
>
> Confusing. That patch is already in 5.18-rc1.
Ahh, my bad, forgot to delete these lines here in the cover letter.
This series just applies cleanly on 5.18-rc1 without dependency.

> But the version which was merged (24e988c7fd1ee701e) lacked the change
> to arch/arm64/Kconfig. I seem to recall that this patch went through a
> few issues and perhaps the arm64 change was dropped. Can you please
> check?

ARCH_HAS_FILTER_PGPROT on arm64 got dropped off via another commit i.e
6e2edd6371a4 ("arm64: Ensure execute-only permissions are not allowed
without EPAN").

>
> (It would be easier for me to track all this down if the original patch
> had had cc:linux-mm. Please cc linux-mm!
Sure, will do. Please do let me know if there is anything else that needs
to be taken care.