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Subject: Re: [PATCH] KVM: PPC: Exit guest upon fatal machine check exception
To: Aravinda Prasad <aravinda@linux.vnet.ibm.com>,
 David Gibson <david@gibson.dropbear.id.au>
References: <20151111165845.3721.98296.stgit@aravindap>
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Cc: kvm@vger.kernel.org, michaele@au1.ibm.com, mahesh@linux.vnet.ibm.com,
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 Daniel Axtens <dja@axtens.net>
From: Thomas Huth <thuth@redhat.com>
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Date: Fri, 13 Nov 2015 08:38:08 +0100
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On 13/11/15 07:26, Aravinda Prasad wrote:
> 
> On Friday 13 November 2015 07:20 AM, David Gibson wrote:
>> On Thu, Nov 12, 2015 at 11:22:29PM +0530, Aravinda Prasad wrote:
[...]
>>> So thinking whether qemu should explicitly enable the new NMI
>>> behavior.
>>
>> So, I think the reasoning above tends towards having qemu control the
>> MC behaviour.  If qemu does nothing, MCs are delivered direct to
>> 0x200, if it enables the new handling, they cause a KVM exit and qemu
>> will deliver the MC.
> 
> This essentially requires qemu to control how KVM behaves as KVM does
> the actual redirection of MC either to guest's 0x200 vector or to exit
> guest. So, if we are running new qemu, then KVM should exit guest and if
> we are running old qemu, KVM should redirect MC to 0x200. Is there any
> way to communicate this to KVM? ioctl?

Simply introduce a KVM capability that can be enabled by userspace.
See kvm_vcpu_ioctl_enable_cap() in arch/powerpc/kvm/powerpc.c.

 Thomas