linux-kernel - Re: [PATCH v4 00/12] mm/debug_vm

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Date:   Mon, 2 Aug 2021 10:23:27 +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,
        akpm@...ux-foundation.org, chuhu@...hat.com, shan.gavin@...il.com,
        Vineet Gupta <vgupta@...opsys.com>
Subject: Re: [PATCH v4 00/12] mm/debug_vm_pgtable: Enhancements



On 8/2/21 5:39 AM, Gavin Shan wrote:
> Hi Anshuman,
> 
> On 7/29/21 5:14 PM, Anshuman Khandual wrote:
>> On 7/27/21 11:43 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 access 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
>>> =========
>>> v4:
>>>     * Determine the page allocation method according to
>>>       MAX_ORDER                                                   (Anshuman)
>>>     * Move existing comments to init_args()                       (Anshuman)
>>>     * Code refactoring as suggested by Anshuman                   (Anshuman)
>>>     * Improved commit log and add comments for flush_dcache_page()
>>>       in PATCH[v4 12/12]                                          (Anshuman)
>>>     * Address misc comments                                       (Anshuman
>>
>> This series builds ok on all supported platforms but should also be tested
>> on them as well i.e s390, ppc, arc and riscv. I was able to do some tests
>> on arm64 and x86 platforms.
>>
> 
> I had tests on the platforms except arc as it's not supported by QEMU yet.
> The test is pretty simple to boot the kernel and see if there is any warning
> raised from mm/debug_vm_pgtable. Everything looks good.

Sure, that should be enough.

> 
> The test was done on v5, which will be posted pretty soon. Thanks again for
> your continuous review.

Please also do copy Vineet Gupta <vgupta@...opsys.com> for ARC in the next version.

- Anshuman