linux-kernel - Re: [PATCH V3] mm/gup: Clear the LRU flag of a page before adding to LRU batch

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] [day] [month] [year] [list]

Message-ID: <dea5afcf-be7d-4377-8b95-754c2f0245c4@126.com>
Date: Thu, 4 Jul 2024 08:57:48 +0800
From: Ge Yang <yangge1116@....com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 21cnbao@...il.com, david@...hat.com, baolin.wang@...ux.alibaba.com,
 aneesh.kumar@...ux.ibm.com, liuzixing@...on.cn
Subject: Re: [PATCH V3] mm/gup: Clear the LRU flag of a page before adding to
 LRU batch



在 2024/7/4 4:08, Andrew Morton 写道:
> On Wed,  3 Jul 2024 20:02:33 +0800 yangge1116@....com wrote:
> 
>> From: yangge <yangge1116@....com>
>>
>> If a large number of CMA memory are configured in system (for example, the
>> CMA memory accounts for 50% of the system memory), starting a virtual
>> virtual machine with device passthrough, it will
>> call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory.
>> Normally if a page is present and in CMA area, pin_user_pages_remote()
>> will migrate the page from CMA area to non-CMA area because of
>> FOLL_LONGTERM flag. But the current code will cause the migration failure
>> due to unexpected page refcounts, and eventually cause the virtual machine
>> fail to start.
>>
>> If a page is added in LRU batch, its refcount increases one, remove the
>> page from LRU batch decreases one. Page migration requires the page is not
>> referenced by others except page mapping. Before migrating a page, we
>> should try to drain the page from LRU batch in case the page is in it,
>> however, folio_test_lru() is not sufficient to tell whether the page is
>> in LRU batch or not, if the page is in LRU batch, the migration will fail.
>>
>> To solve the problem above, we modify the logic of adding to LRU batch.
>> Before adding a page to LRU batch, we clear the LRU flag of the page so
>> that we can check whether the page is in LRU batch by folio_test_lru(page).
>> Seems making the LRU flag of the page invisible a long time is no problem,
>> because a new page is allocated from buddy and added to the lru batch,
>> its LRU flag is also not visible for a long time.
>>
> 
> Thanks.
> 
> I'll add this to the mm-hotfixes branch for additional testing.  Please
> continue to work with David on the changelog enhancements.
> 
> In mm-hotfixes I'd expect to send it to Linus next week.  I could move
> it into mm-unstable (then mm-stable) for merging into 6.11-rc1.  This
> is for additional testing time - it will still be backported into
> earlier kernels.  We can do this with any patch.

Ok, thanks.