Re: [Qemu-devel] kvm bug in __rmap_clear_dirty during live migration

[Chris Friesen]

On 02/22/2017 05:15 AM, Paolo Bonzini wrote:
> On 22/02/2017 04:08, Chris Friesen wrote:
> > On 02/19/2017 10:38 PM, Han, Huaitong wrote:
> > > Hi, Gaohuai
> > >
> > > I tried to debug the problem, and I found the indirect cause may be that
> > > the rmap value is not cleared when KVM mmu page is freed. I have read
> > > code without the root cause. Can you stable reproduce the the issue?
> > > Many guesses need to be verified.
> >
> > In both cases it seems to have been triggered by repeatedly
> > live-migrating a KVM virtual machine between two hypervisors with
> > Broadwell CPUs running the latest CentOS 7.
> >
> > It's a race of some sort, it doesn't happen every time.
>
> Can you reproduce it with kernel 4.8+?  I'm suspecting commmit
> 4e59516a12a6 ("kvm: vmx: ensure VMCS is current while enabling PML",
> 2016-07-14) to be the fix.

I can't easily try with a newer kernel, the software package we're using has 
kernel patches that would have to be ported.

I'm at a conference, don't really have time to set up a pair of test machines 
from scratch with a custom kernel.

Chris