kvm-hint-dedicated requires host CPU passthrough?

[Stefan Hajnoczi]

On Wed, May 20, 2020 at 07:23:32PM +0200, Paolo Bonzini wrote:
> On 20/05/20 19:13, Stefan Hajnoczi wrote:
> > Hi,
> > libvirt refuses to set KVM_HINTS_DEDICATED when the CPU model is not
> > host-passthrough.
> > 
> > Is there a reason for this limitation?
> > 
> > My understanding is that KVM_HINTS_DEDICATED means the vCPU is pinned to
> > a host CPU that is not shared with other tasks. Any KVM vCPU should be
> > able to support this feature, regardless of whether host-passthrough is
> > used or not.
> 
> Perhaps it's because KVM_HINTS_DEDICATED enables mwait passthrough, and
> the details of mwait vary per CPU model?

KVM_HINTS_DEDICATED (now known as KVM_HINTS_REALTIME) is also used by
cpuidle-haltpoll. In that case we don't care about mwait.

CPU passthrough can prevent live migration, so I think we should relax
this check, if possible.

Wim: Can you let us know what the original intention of checking for
cpu-passthrough was?

Thanks,
Stefan
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