Re: Migration failure when running nested VMs

[Paolo Bonzini]

On 23/09/19 20:32, Jintack Lim wrote:
> On Mon, Sep 23, 2019 at 4:48 AM Paolo Bonzini <address@hidden> wrote:
>>
>> On 23/09/19 12:42, Dr. David Alan Gilbert wrote:
>>>
>>> With those two clues, I guess maybe some dirty pages made by L2 are
>>> not transferred to the destination correctly, but I'm not really sure.
>>>
>>> 3) It happens on Intel(R) Xeon(R) Silver 4114 CPU, but it does not on
>>> Intel(R) Xeon(R) CPU E5-2630 v3 CPU.
>>
>> Hmm, try disabling pml (kvm_intel.pml=0).  This would be the main
>> difference, memory-management wise, between those two machines.
>>
> 
> Thank you, Paolo.
> 
> This makes migration work successfully over 20 times in a row on
> Intel(R) Xeon(R) Silver 4114 CPU where migration failed almost always
> without disabling pml.
> 
> I guess there's a problem in KVM pml code? I'm fine with disabling
> pml. But if you have patches to fix the issue, I'm willing to test it
> on the CPU.

Yes, it's a known bug in the PML code (that I thought was not an issue
for migration, but I was wrong).  I'll try to get you a patch this week.

Paolo