Re: [Qemu-devel] -cpu check, rdtscp and AMD KVM

[Paolo Bonzini]

On 12/11/2015 17:27, Eduardo Habkost wrote:
>> > > To simply remove rdtscp from all Opteron_G* models?
> > 
> > Not sure this is the right thing to do...  Real hardware has it, and
> > going forward KVM will provide it.
> 
> Do you see any alternative?

Live with the warning, and document it in the release notes.

> We need AMD CPU models that can run
> out of the box using today's kernels. As no existing VMs running
> Opteron_G* on AMD CPUs have rdtscp, I believe it makes sense to
> just define Opteron_G* without rdtscp.
> 
> When we add SVM rdtscp support to KVM, we can add new
> "Opteron_G[2-5]-rdtscp" CPU models.

Makes sense too.

However, I'm a bit afraid of the interaction with libvirt. Right now,
libvirt has rdtscp in the description.  If we remove it from libvirt,
libvirt will start adding +rdtscp to the QEMU CPU command line option,
so our change will be moot.  And if we do not remove it from libvirt,
libvirt will not be able to start a VM with rdtscp on a fixed kernel.

Is this correct?

Paolo