Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 12 Apr 2023 15:56:18 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Liu Shixin <liushixin2@huawei.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Tony Luck <tony.luck@intel.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Muchun Song <muchun.song@linux.dev>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] mm: hwpoison: support recovery from HugePage
 copy-on-write faults
Message-Id: <20230412155618.720e6b3aa5be6444f7889ea6@linux-foundation.org>
In-Reply-To: <20230412222138.GB4759@monkey>
References: <20230411092741.780679-1-liushixin2@huawei.com>
        <20230412181350.GA22818@monkey>
        <20230412145718.0bcb7dd98112a3010711ad0b@linux-foundation.org>
        <20230412222138.GB4759@monkey>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Wed, 12 Apr 2023 15:21:38 -0700 Mike Kravetz <mike.kravetz@oracle.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?