Re: [Qemu-ppc] [Qemu-devel] [PATCH 4/4] target-ppc: Handle NMI guest exit

[Aravinda Prasad]

On Monday 16 November 2015 02:31 PM, Thomas Huth wrote:
> On 16/11/15 04:50, Paul Mackerras wrote:
>> On Thu, Nov 12, 2015 at 09:09:59AM +0100, Thomas Huth wrote:
>>>
>>> Shouldn't you also check MSR_ME here first and enter checkstop when
>>> machine checks are disabled?
>>
>> MSR_ME is a hypervisor resource and is not able to be controlled by HV
>> KVM guests, or in fact by the OS running on the pseries machine target
>> regardless of how it's accelerated or emulated.
>>
>> What you say would only apply if we had a powernv machine target and
>> we were emulating the whole system, and in that case we wouldn't be
>> using any hcalls, and we wouldn't be doing FWNMI (or at least not at
>> this level).
>>
>> So the answer is no, MSR_ME will always be set when running in a
>> guest, and we don't ever need to checkstop the virtual machine.
> 
> Good point, I missed that sentence about the hypervisor resource in the
> PowerISA. So QEMU does not have to check this bit here.
> 
> But out of curiosity: What happens if a guest disables the ME bit? Is
> this checked somewhere or simply ignored?

If a guest disables the ME bit (and may be does not set it again) and
should a machine check happen in guest address space then the entire
system checkstops? However, I am not sure if the guest is allowed to
disable ME bit.

Regards,
Aravinda

> 
>  Thomas
> 

-- 
Regards,
Aravinda