linux-kernel - Re: [PATCH v5 00/12] mm/debug_vm

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Date:   Tue, 3 Aug 2021 12:20:24 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, gerald.schaefer@...ux.ibm.com,
        aneesh.kumar@...ux.ibm.com, christophe.leroy@...roup.eu,
        cai@....pw, catalin.marinas@....com, will@...nel.org,
        vgupta@...opsys.com, akpm@...ux-foundation.org, chuhu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v5 00/12] mm/debug_vm_pgtable: Enhancements



On 8/2/21 11:34 AM, Gavin Shan wrote:
> There are couple of issues with current implementations and this series
> tries to resolve the issues:
> 
>   (a) All needed information are scattered in variables, passed to various
>       test functions. The code is organized in pretty much relaxed fashion.
> 
>   (b) The page isn't allocated from buddy during page table entry modifying
>       tests. The page can be invalid, conflicting to the implementations
>       of set_xxx_at() on ARM64. The target page is accessed so that the
>       iCache can be flushed when execution permission is given on ARM64.
>       Besides, the target page can be unmapped and accessing to it causes
>       kernel crash.
> 
> "struct pgtable_debug_args" is introduced to address issue (a). For issue
> (b), the used page is allocated from buddy in page table entry modifying
> tests. The corresponding tets will be skipped if we fail to allocate the
> (huge) page. For other test cases, the original page around to kernel
> symbol (@start_kernel) is still used.
> 
> The patches are organized as below. PATCH[2-10] could be combined to one
> patch, but it will make the review harder:
> 
>   PATCH[1] introduces "struct pgtable_debug_args" as place holder of all
>            needed information. With it, the old and new implementation
>            can coexist.
>   PATCH[2-10] uses "struct pgtable_debug_args" in various test functions.
>   PATCH[11] removes the unused code for old implementation.
>   PATCH[12] fixes the issue of corrupted page flag for ARM64
> 
> Changelog
> =========
> v5:
>    * Pick r-bs from Anshuman and rebase to 5.14.rc4          (Gavin)
>    * Use args->start_p4dp to free p4d entries                (Anshuman)
>    * Introduce helper to allocate huge page in init_arg()    (Anshuman)
>    * Bail early if the allocated page doesn't exist in
>      swap_migration_tests() and correct the comments         (Anshuman)
>    * Add fixes tag to PATCH[v4 12/12]                        (Christophe)
>    * Address misc comments                                   (Anshuman)

Apart from the proposed changes discussed for the first patch [PATCH 1/12],
this series overall looks good now. It clears build tests on all supported
platforms. I was able to test this on arm64 and x86 platforms with various
functional config combinations. It would be still great if others can take
a look as well.

- Anshuman