linux-kernel - Re: kvm splat in mmu_spte_clear_track

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Date:   Tue, 29 Aug 2017 09:10:59 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Adam Borowski <kilobyte@...band.pl>, Takashi Iwai <tiwai@...e.de>,
        Bernhard Held <berny156@....de>,
        Nadav Amit <nadav.amit@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: kvm splat in mmu_spte_clear_track_bits

On Tue, Aug 29, 2017 at 7:09 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
> Hello,
>
> On Tue, Aug 29, 2017 at 02:59:23PM +0200, Adam Borowski wrote:
>> On Tue, Aug 29, 2017 at 02:45:41PM +0200, Takashi Iwai wrote:
>> > [Put more people to Cc, sorry for growing too much...]
>>
>> We're all interested in 4.13.0 not crashing on us, so that's ok.
>>
>> > On Tue, 29 Aug 2017 11:19:13 +0200,
>> > Bernhard Held wrote:
>> > >
>> > > On 08/28/2017 at 06:56 PM, Nadav Amit wrote:
>> > > > Don’t blame me for the TLB stuff... My money is on aac2fea94f7a .
>> > >
>> > > Amit, thanks for your courage to expose your patch!
>> > >
>> > > I'm more and more confident that aac2fea94f7a is the culprit.  Maybe it
>> > > just accelerates the triggering of the splash.  To be more sure the
>> > > kernel needs to be tested for a couple of days.  It would be great if
>> > > others could assist in testing aac2fea94f7a.
>> >
>> > I'm testing with the revert for a while and it seems working.
>>
>> With nothing but aac2fea94f7a reverted, no explosions for me either.
>
> The aforementioned commit has 3 bugs.

Yes. I'm reverting it from my tree.

We should really *really* just tell the stupid MMU notifier users that
they can't sleep.

The MMU notifiers are not going to destroy our VM layer. I hate the
damn crap, and this kind of garbage is an example of why.

So Andrew - please stop taking "MMU notifier can sleep" patches. Start
taking patches that fix the users, not break the VM.

                    Linus