linux-kernel - Re: [PATCH] hugetlbfs: don't delete error page from pagecache

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Date:   Mon, 7 Nov 2022 04:25:45 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
CC:     James Houghton <jthoughton@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Shi <shy828301@...il.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hugetlbfs: don't delete error page from pagecache

On Fri, Nov 04, 2022 at 06:27:44AM -0700, Mike Kravetz wrote:
> On 11/04/22 02:10, HORIGUCHI NAOYA(堀口 直也) wrote:
> > On Tue, Oct 18, 2022 at 08:01:25PM +0000, James Houghton wrote:
> > > This change is very similar to the change that was made for shmem [1],
> > > and it solves the same problem but for HugeTLBFS instead.
> > > 
> > > Currently, when poison is found in a HugeTLB page, the page is removed
> > > from the page cache. That means that attempting to map or read that
> > > hugepage in the future will result in a new hugepage being allocated
> > > instead of notifying the user that the page was poisoned. As [1] states,
> > > this is effectively memory corruption.
> > > 
> > > The fix is to leave the page in the page cache. If the user attempts to
> > > use a poisoned HugeTLB page with a syscall, the syscall will fail with
> > > EIO, the same error code that shmem uses. For attempts to map the page,
> > > the thread will get a BUS_MCEERR_AR SIGBUS.
> > > 
> > > [1]: commit a76054266661 ("mm: shmem: don't truncate page if memory failure happens")
> > > 
> > > Signed-off-by: James Houghton <jthoughton@...gle.com>
> > 
> > I did some testing and found no issue. So I agree with this patch.
> > Thank you very much.
> > 
> > Tested-by: Naoya Horiguchi <naoya.horiguchi@....com>
> > Reviewed-by: Naoya Horiguchi <naoya.horiguchi@....com>
> > 
> > As for whether to go with HGM patchset or not, I have no strong opinion.
> > As you stated in another email this patch is correct without HGM patch,
> > so it's OK to me to make this merged first.
> 
> Thanks Naoya.
> 
> This is a late thought, but ...
> Should this patch and Yang Shi's shmem patch be backported to stable releases?
> Both address potential data corruption/loss, so it certainly seems like
> stable material.

Yes, I agree that backporting these could be helpful.

So I think that I'll try to backport commit a7605426666 and its dependencies
to 5.15 (and older LTS if possible).  For this patch, just adding "Cc: stable"
should be enough for now.

Thanks,
Naoya Horiguchi