linux-kernel - Re: [PATCH 1/8] KVM: SVM: Fix nested nmi handling

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Message-Id: <CEE68C62-43B0-406C-9426-6201901022AF@suse.de>
Date:	Fri, 23 Apr 2010 21:18:15 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] KVM: SVM: Fix nested nmi handling


On 23.04.2010, at 16:51, Joerg Roedel wrote:

> On Fri, Apr 23, 2010 at 04:42:52PM +0200, Alexander Graf wrote:
>> 
>> On 23.04.2010, at 16:31, Joerg Roedel wrote:
>> 
>>> On Fri, Apr 23, 2010 at 04:24:54PM +0200, Alexander Graf wrote:
>>>> 
>>>> On 23.04.2010, at 16:22, Joerg Roedel wrote:
>>> 
>>>>> No, nested_svm_nmi runs in atomic context where we can't emulate a
>>>>> vmexit. We set exit_required and emulate the vmexit later.
>>>> 
>>>> So we modify the L2 rflags and then trigger a #vmexit, leaving the l2
>>>> state broken?
>>> 
>>> No, the rflags are changed in enable_nmi_window which isn't called when
>>> we run nested and the nested hypervisor intercepts nmi. So it only runs
>>> in the !nested case where it can't corrupt L2 state.
>> 
>> Last time I checked the code enable_nmi_window was the function
>> triggering the #vmexit,
> 
> Yes, thats the bug which this patch fixes :-)
> 
>> so it should run in that exact scenario. If what you say is true, where
>> do we #vmexit instead then?
> 
> After setting exit_required we run into svm.c:svm_vcpu_run. There the
> exit_required flag is checked and if set, the function immediatly
> returns without doing a vmrun. A few cycles later we run into
> svm.c:handle_exit() where at the beginning exit_required is checked, and
> if set the vmexit is emulated.

Oh well, I guess I have to trust you on this one :)


Alex

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