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From: Thomas Huth <thuth@redhat.com>
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Date: Mon, 16 Nov 2015 10:01:25 +0100
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Subject: Re: [Qemu-devel] [PATCH 4/4] target-ppc: Handle NMI guest exit
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To: Paul Mackerras <paulus@ozlabs.org>
Cc: benh@au1.ibm.com, aik@ozlabs.ru, agraf@suse.de, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Aravinda Prasad <aravinda@linux.vnet.ibm.com>, sam.bobroff@au1.ibm.com, david@gibson.dropbear.id.au

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?
>=20
> 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.
>=20
> 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).
>=20
> 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?

 Thomas