Re: fedora 10 x86_64 breakage under KVM, due to KVM_CLOCK

From: Lennert Buytenhek <buytenh@wantstofly.org>
To: Avi Kivity <avi@redhat.com>
Cc: kvm@vger.kernel.org, lfarkas@lfarkas.org, davej@codemonkey.org.uk
Subject: Re: fedora 10 x86_64 breakage under KVM, due to KVM_CLOCK
Date: Sat, 25 Apr 2009 23:30:11 +0200	[thread overview]
Message-ID: <20090425213011.GW14729@mail.wantstofly.org> (raw)
In-Reply-To: <49EC62DC.5080900@redhat.com>

On Mon, Apr 20, 2009 at 02:56:12PM +0300, Avi Kivity wrote:

> >Fedora 10 randomly hangs for me when run under KVM, whereas (unpatched)
> >F9 works fine.  When this happens, kvm_stat shows that the VM is seeing
> >1000 IRQ exits per second, but nothing else seems to happen.  The latest
> >F9 update kernel seems to be bust as well.  (I noticed that the KVM guest
> >support status page says that "Alexey E." is seeing the same thing.)
> >
> >I tried about two dozen different kernel packages from koji, and it turns
> >out that kernel-2.6.26-0.122.rc9.git4.fc10 is the last known good kernel,
> >and kernel-2.6.26-0.124.rc9.git5.fc10 is the first kernel that's broken.
> >
> >The F10 instability appears since this commit (attached below as well):
> >
> >	http://fedora.gitbits.net/?p=kernel;a=commit;h=a5991f36968f44d4d3c64fc5aaa285a21de1ba54
> >
> >I built three new kernels from the latest 2.6.27-170.2.56.fc10 update
> >in Fedora 10:
> >1. One with PARAVIRT and all associated options disabled entirely.
> >2. One with only KVM_GUEST disabled.
> >3. One with only KVM_CLOCK disabled (and paravirt and KVM_GUEST enabled).
> >
> >Kernel (1) is stable.  Kernel (2) is unstable like the unpatched F10
> >kernels are, in that it randomly locks up.  Kernel (3) is stable as
> >well, which suggests that KVM_CLOCK is what's causing the lockups.
> >
> >I tried booting the original F10 update kernel with no-kvmclock on
> >the command line as well, and that makes things stable as well.
> >
> >I tried with the latest F10 updates-testing kernel (2.6.29.1-30.fc10),
> >and that shows the same thing: with no-kvmclock it works fine, otherwise
> >it hangs randomly.
> >
> >Running KVM 84 on x86_64 CentOS 5.3, with the kvm rpms from lfarkas.org.
> >The host CPU is a Q6600 Core 2 Quad.
> >
> >Any ideas?
> 
> This is a known issue.  While kvm-84 fixed kvmclock, an issue remained 
> with cpu frequency scaling on older host kernels (including RHEL 5 / 
> CentOS 5).  kvm-85 (to be released shortly) contains a fix (b395d156477a 
> in kvm-userspace.git).

Seems to work fine, thanks!