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Subject: Re: VMs freezing when host is running 4.14
To:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Marc Haber <mh+linux-kernel@zugschlus.de>
Cc:     =?UTF-8?B?546L6YeR5rWm?= <jinpuwang@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "KVM-ML (kvm@vger.kernel.org)" <kvm@vger.kernel.org>,
        x86@kernel.org
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 <20180108091025.2sup55jlpzbouo3d@torres.zugschlus.de>
 <20180211133941.gayg52r3bqbtptvm@torres.zugschlus.de>
 <20180214020445.ebu4fhnmogqehunb@treble>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <62aa6b81-5456-07dc-cf64-e46747d3a70d@redhat.com>
Date:   Wed, 14 Feb 2018 11:23:44 +0100
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On 14/02/2018 03:04, Josh Poimboeuf wrote:
> On Sun, Feb 11, 2018 at 02:39:41PM +0100, Marc Haber wrote:
>> Hi,
>>
>> after in total nine weeks of bisecting, broken filesystems, service
>> outages (thankfully on unportant systems), 4.15 seems to have fixed the
>> issue. After going to 4.15, the crashes never happened again.
>>
>> They have, however, happened with each and every 4.14 release I tried,
>> which I stopped doing with 4.14.15 on Jan 28.
>>
>> This means, for me, that the issue is fixed and that I have just wasted
>> nine weeks of time.
>>
>> For you, this means that you have a crippling, data-eating issue in the
>> current long-term releae kernel. I do sincerely hope that I never have
>> to lay my eye on any 4.14 kernel and hope that no major distribution
>> will release with this version.
> 
> I saw something similar today, also in kvm_async_pf_task_wait().  I had
> -tip in the guest (based on 4.16.0-rc1) and Fedora
> 4.14.16-300.fc27.x86_64 on the host.

Hi Josh/Marc,

this is fixed by

    commit 2a266f23550be997d783f27e704b9b40c4010292
    Author: Haozhong Zhang <haozhong.zhang@intel.com>
    Date:   Wed Jan 10 21:44:42 2018 +0800

    KVM MMU: check pending exception before injecting APF
    
    For example, when two APF's for page ready happen after one exit and
    the first one becomes pending, the second one will result in #DF.
    Instead, just handle the second page fault synchronously.
    
    Reported-by: Ross Zwisler <zwisler@gmail.com>
    Message-ID: <CAOxpaSUBf8QoOZQ1p4KfUp0jq76OKfGY4Uxs-Gg8ngReD99xww@mail.gmail.com>
    Reported-by: Alec Blayne <ab@tevsa.net>
    Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

and it will be in 4.14.20.  Unfortunately I only heard about this issue
last week.

Thanks,

Paolo