[v2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[RFT PATCH v2 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

Posted by Hector Cao 3 days, 6 hours ago

Thanks Paolo for the great improvements you made to the original POC
patches,

I can confirm that the migration we had for Intel CPU (Haswell) is fixed
with these 2 patches.

I can see that for arch-capabilities, in addition to the
compatibility property, you did slightly change
the behavior by limiting it to AMD CPU (other x86 CPUs like Intel will have
the old behavior prior 10.1 so no migration issue).
Do you think it is good to make it clear in the commit log ?

I'm also trying to test on an AMD CPU and will report back.

Thanks,
Hector

Re: [RFT PATCH v2 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

Posted by Paolo Bonzini 5 hours ago

On 9/25/25 10:40, Hector Cao wrote:
> I can confirm that the migration we had for Intel CPU (Haswell) is fixed 
> with these 2 patches.

Great, thanks for testing.

> I can see that for arch-capabilities, in addition to the 
> compatibility property, you did slightly change
> the behavior by limiting it to AMD CPU (other x86 CPUs like Intel will 
> have the old behavior prior 10.1 so no migration issue).
> Do you think it is good to make it clear in the commit log ?

Sure:

     To preserve the functionality (added by 10.1) of turning off
     ARCH_CAPABILITIES where Windows does not like it, use directly
     the guest CPU vendor: x86_cpu_get_supported_feature_word is not
     KVM-specific and therefore should not necessarily use the host
     CPUID.

Paolo