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

[Chris Friesen <chris.friesen@windriver.com>]

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