linux-kernel - Re: [PATCH v2 1/2] selftests: khugepaged: fix the shmem collapse failure

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <89a2645b-41fe-4717-a08f-1270d8da0863@arm.com>
Date: Fri, 13 Jun 2025 09:03:38 +0530
From: Dev Jain <dev.jain@....com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 david@...hat.com
Cc: lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, baohua@...nel.org, shuah@...nel.org, ziy@...dia.com,
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] selftests: khugepaged: fix the shmem collapse
 failure


On 13/06/25 7:19 am, Baolin Wang wrote:
> When running the khugepaged selftest for shmem (./khugepaged all:shmem),
> I encountered the following test failures:
> "
> Run test: collapse_full (khugepaged:shmem)
> Collapse multiple fully populated PTE table.... Fail
> ...
> Run test: collapse_single_pte_entry (khugepaged:shmem)
> Collapse PTE table with single PTE entry present.... Fail
> ...
> Run test: collapse_full_of_compound (khugepaged:shmem)
> Allocate huge page... OK
> Split huge page leaving single PTE page table full of compound pages... OK
> Collapse PTE table full of compound pages.... Fail
> "
>
> The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
> khugepaged from continuing to scan shmem VMA after khugepaged finishes
> scanning in the wait_for_scan() function. Moreover, shmem requires a refault
> to establish PMD mappings.
>
> However, after commit 2b0f922323cc ("mm: don't install PMD mappings when
> THPs are disabled by the hw/process/vma"), PMD mappings are prevented if the
> VMA is set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings
> during refault.
>
> One way to fix this issue is to move the MADV_NOHUGEPAGE setting after the
> shmem refault. After shmem refault and check huge, the test case will unmap
> the shmem immediately. So it seems unnecessary to set the MADV_NOHUGEPAGE.
>
> Then we can simply drop the MADV_NOHUGEPAGE setting, and all khugepaged test
> cases passed.
>
> Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the hw/process/vma")
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---

The test converts from fail to pass for me, for the aforementioned failures.

Reviewed-by: Dev Jain <dev.jain@....com>
Tested-by: Dev Jain <dev.jain@....com>

>