Re: [PATCH v4 1/3] target-i386: KVM: add basic Intel LMCE support

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Jun 16, 2016 at 12:42:19PM +0200, Paolo Bonzini wrote:
> 
> 
> On 16/06/2016 12:34, Haozhong Zhang wrote:
> > On 06/16/16 12:23, Paolo Bonzini wrote:
> >>
> >>
> >> On 16/06/2016 12:16, Haozhong Zhang wrote:
> >>>>
> >>>>> +        has_msr_mcg_ext_ctl = true;
> >>>>>      }
> >>>>>  
> >>>>>      c = cpuid_find_entry(&cpuid_data.cpuid, 0x80000007, 0);
> >>>>
> >>>> Which silicon has LMCE?  We may want to enable the property for some CPU
> >>>> models.  Apart from this, the patch is pretty much okay.
> >>>
> >>> Skylake-EX
> >>
> >> ... However, all virtual CPUs can use LMCE because the rendez-vous is
> >> done in the host.  Is this correct?
> >>
> > 
> > Yes, if it does not confuse the guest which sees LMCE available on
> > lower end or earlier CPUs (though I think someone would feel
> > happy).
> 
> Yes, that's what I expect too.  No confusion, and some happiness. :)
> 
> > Or do we add it only to qemu64 and kvm64?
> 
> I'm not sure where to add it, actually. :(  Let's wait for Eduardo's
> opinion.

Unfortunately we can't enable it by default to any existing CPU
model, or we break the machine-type-runnability rule
(machine-type version changes in an existing runnable VM
configuration should never make the VM not runnable in the same
host).

If one day we decide that QEMU as a whole can require a newer
kernel, then we can enable it by default on all CPU models.

What's the first kernel release where LMCE is enabled in
KVM_X86_GET_MCE_CAP_SUPPORTED, BTW?

-- 
Eduardo