Re: [Qemu-devel] [PULL 22/25] target/i386: kvm: Add nested migration blocker only when kernel lacks required capabilities

[Liran Alon]

> On 21 Jun 2019, at 20:27, Paolo Bonzini <address@hidden> wrote:
> 
> On 21/06/19 17:07, Liran Alon wrote:
>>> So, overall I prefer not to block migration.
>> I’m not sure I agree.
>> It is quite likely that vCPU is currently in guest-mode while you are 
>> migrating…
>> A good hypervisor tries to maximise CPU time to be in guest-mode rather than 
>> host-mode. :)
> 
> True, but it is even more likely that they are not using KVM at all and
> just happen to have the CPUID flag set. :)
> 
> Paolo

Since QEMU commit 75d373ef9729 ("target-i386: Disable SVM by default in KVM 
mode"),
An AMD vCPU that is virtualized by KVM don’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 any nSVM
workload inside guest. Unless I’m missing something obvious.
Otherwise, I would have agreed with you.

-Liran