linux-kernel - Re: [GIT PULL] First batch of KVM changes for 4.1

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Date:	Wed, 22 Apr 2015 18:21:48 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...nel.org>, kvm list <kvm@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Andrew Lutomirski <luto@...nel.org>
Subject: Re: [GIT PULL] First batch of KVM changes for 4.1

On Mon, Apr 20, 2015 at 01:27:58PM -0700, Andy Lutomirski wrote:
> On Mon, Apr 20, 2015 at 9:59 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> >
> >
> > On 17/04/2015 22:18, Marcelo Tosatti wrote:
> >> The bug which this is fixing is very rare, have no memory of a report.
> >>
> >> In fact, its even difficult to create a synthetic reproducer.
> >
> > But then why was the task migration notifier even in Jeremy's original
> > code for Xen?  Was it supposed to work even on non-synchronized TSC?
> >
> > If that's the case, then it could be reverted indeed; but then why did
> > you commit this patch to 4.1?  Did you think of something that would
> > cause the seqcount-like protocol to fail, and that turned out not to be
> > the case later?  I was only following the mailing list sparsely in March.
> 
> I don't think anyone ever tried that hard to test this stuff.  There
> was an infinte loop that Firefox was triggering as a KVM guest
> somewhat reliably until a couple months ago in the same vdso code.  :(

https://bugzilla.redhat.com/show_bug.cgi?id=1174664

--- Comment #5 from Juan Quintela <quintela@...hat.com> ---

Another round

# dmesg | grep msr
[    0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[    0.000000] kvm-clock: cpu 0, msr 1:1ffd8001, primary cpu clock
[    0.000000] kvm-stealtime: cpu 0, msr 11fc0d100
[    0.041174] kvm-clock: cpu 1, msr 1:1ffd8041, secondary cpu clock
[    0.053011] kvm-stealtime: cpu 1, msr 11fc8d100


After start:

[root@...sno yum.repos.d]# virsh qemu-monitor-command --hmp browser  'xp
/8x
0x1ffd8000'
000000001ffd8000: 0x3b401060 0xfffc7f4b 0x3b42d040 0xfffc7f4b
000000001ffd8010: 0x3b42d460 0xfffc7f4b 0x3b42d4c0 0xfffc7f4b


[root@...sno yum.repos.d]# virsh qemu-monitor-command --hmp browser  'xp /8x 0x1ffd8040'
000000001ffd8040: 0x3b42d700 0xfffc7f4b 0x3b42d760 0xfffc7f4b
000000001ffd8050: 0x3b42d7c0 0xfffc7f4b 0x3b42d820 0xfffc7f4b

When firefox hangs

[root@...sno yum.repos.d]# virsh qemu-monitor-command --hmp browser  'xp
/8x
0x1ffd8000'
000000001ffd8000: 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a
000000001ffd8010: 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a


[root@...sno yum.repos.d]# virsh qemu-monitor-command --hmp browser  'xp
/8x
0x1ffd8040'
000000001ffd8040: 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a
000000001ffd8050: 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a 0x5a5a5a5a


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