Re: [Qemu-devel] [PATCH 0/2] target/i386: kvm: Fix treatment of AMD SVM in nested migration

[Liran Alon]

> On 22 Jun 2019, at 2:59, Paolo Bonzini <address@hidden> wrote:
> 
> On 21/06/19 23:37, Liran Alon wrote:
>> However, during discussion made after merge, it was realised that since QEMU 
>> commit
>> 75d373ef9729 ("target-i386: Disable SVM by default in KVM mode"), an AMD 
>> vCPU that
>> is virtualized by KVM doesn't expose SVM by default, even if you use "-cpu 
>> host".
>> Therefore, it is unlikely that vCPU expose SVM CPUID flag when user is not 
>> running
>> an SVM workload inside guest.
> 
> libvirt has "host-model" mode, which constructs a "-cpu
> model,+feature,+feature" command line option that matches the host as
> good as possible.  This lets libvirt check migratability while retaining
> a lot of the benefits of "-cpu host", and is the default for OpenStack
> for example.  I need to check if libvirt adds SVM to this configuration,
> if it does the QEMU commit you mention is unfortunately not enough.
> 
> Paolo

Hmm nice catch. I haven’t thought about it (Not familiar much with libvirt).
I agree that if libvirt adds SVM to this configuration than we must not block
migration for an AMD vCPU that is exposed with SVM… :(

Please update once you figure out libvirt behaviour regarding this,
-Liran