Re: [PATCH 1/2] KVM: Expose MCE control MSRs to userspace

[Avi Kivity <avi@redhat.com>]

On 07/08/2010 11:03 AM, Huang Ying wrote:
> On Thu, 2010-07-08 at 15:43 +0800, Avi Kivity wrote:
>    
>> On 07/08/2010 05:07 AM, Huang Ying wrote:
>>      
>>>        
>>>>    static u32 emulated_msrs[] = {
>>>>    	MSR_IA32_MISC_ENABLE,
>>>> +	MSR_IA32_MCG_STATUS,
>>>> +	MSR_IA32_MCG_CTL,
>>>>
>>>>          
>>> We need only clear MSR_IA32_MCG_STATUS during reset, but should not
>>> clear MSR_IA32_MCG_CTL.
>>>
>>>
>>>        
>> Why not?
>>      
> According to Intel 64 and IA32 Architectures Software Developer's Manual
> (SDM) Vol 3A (Table 9-1), machine check MSRs should be sticky across
> reset.


Well, my copy says:

     Machine-Check Architecture   Pwr up or Reset:  Undefined          
INIT: Unchanged

So it seems we're free to clear it.  But probably the best thing would 
be to have the bios initialize it to disabled state?

Note, in any case we have to expose the MSRs for live migration.

> Except we need some special processing for MSR_IA32_MCG_STATUS.
>    

What do you have in mind?

> And if we clear MSR_IA32_MCG_CTL, the machine check reporting is
> disabled according to SDM Vol 3A, section 15.3.1.3
>    

Won't the kernel reenable MCE?  In my testing, the sequence 
MCE-reset-MCE worked after the patch (whereas it would fail without it).

-- 
error compiling committee.c: too many arguments to function