linux-kernel - Re: [PATCH] [2/2] KVM: Add VT-x machine check support

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Date:	Thu, 4 Jun 2009 15:01:07 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, ying.huang@...el.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [2/2] KVM: Add VT-x machine check support

On Thu, Jun 04, 2009 at 03:49:03PM +0300, Avi Kivity wrote:
> Andi Kleen wrote:
> >>This assumption is incorrect.  This code is executed after preemption 
> >>has been enabled, and we may have even slept before reaching it.
> >>    
> >
> >The only thing that counts here is the context before the machine
> >check event. If there was a vmexit we know it was in guest context.
> >
> >The only requirement we have is that we're running still on the same
> >CPU. I assume that's true, otherwise the vmcb accesses wouldn't work?
> >  
> 
> It's not true, we're in preemptible context and may have even slept.
> 
> vmcs access work because we have a preempt notifier called when we are 
> scheduled in, and will execute vmclear/vmptrld as necessary.  Look at 
> kvm_preempt_ops in virt/kvm_main.c.

I see. So we need to move that check earlier. Do you have a preference
where it should be?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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