linux-kernel - Re: [PATCH -next] mm: hwpoison: support recovery from HugePage copy-on-write faults

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Message-Id: <20230412155618.720e6b3aa5be6444f7889ea6@linux-foundation.org>
Date:   Wed, 12 Apr 2023 15:56:18 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Liu Shixin <liushixin2@...wei.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Tony Luck <tony.luck@...el.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] mm: hwpoison: support recovery from HugePage
 copy-on-write faults

On Wed, 12 Apr 2023 15:21:38 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> > > Commit a873dfe1032a ("mm, hwpoison: try to recover from copy-on write
> > > faults") introduced the routine copy_user_highpage_mc() to gracefully
> > > handle copying of user pages with uncorrectable errors.  Previously,
> > > such copies would result in a kernel crash.  hugetlb has separate code
> > > paths for copy-on-write and does not benefit from the changes made in
> > > commit a873dfe1032a.
> 
> I was just going to suggest adding the line,
> 
> Hence, copy-on-write of hugetlb user pages with uncorrectable errors            
> will result in a kernel crash as was the case with 'normal' pages before        
> commit a873dfe1032a.
> 
> However, I'm guessing it might be more clear if we start with the
> runtime effects.  Something like:
> 
> copy-on-write of hugetlb user pages with uncorrectable errors will result
> in a kernel crash.  This is because the copy is performed in kernel mode
> and in general we can not handle accessing memory with such errors while
> in kernel mode.  Commit a873dfe1032a ("mm, hwpoison: try to recover from
> copy-on write faults") introduced the routine copy_user_highpage_mc() to
> gracefully handle copying of user pages with uncorrectable errors.  However,
> the separate hugetlb copy-on-write code paths were not modified as part
> of commit a873dfe1032a.

Sounds good.  So I assume cc:stable is desirable.

I can't actually get the patch to apply to anything.  Can we please
have a redo against current -linus?