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

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/06/2016 20:05, Eduardo Habkost wrote:
> 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?

It will presumably be 4.8.

Paolo