linux-kernel - Re: [PATCH V4 0/7] mm/mmap: Drop arch_vm_get_page_prot() and arch_filter

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Message-ID: <a84bdc2a-2656-0474-4a14-5532c29f9043@arm.com>
Date:   Fri, 8 Apr 2022 08:11:38 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Christoph Hellwig <hch@...radead.org>,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, sparclinux@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 0/7] mm/mmap: Drop arch_vm_get_page_prot() and
 arch_filter_pgprot()



On 4/8/22 04:50, Andrew Morton wrote:
> On Thu,  7 Apr 2022 16:02:44 +0530 Anshuman Khandual <anshuman.khandual@....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.