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

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Date:	Thu, 04 Jun 2009 15:49:03 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	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

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.

>> We get both an explicit EXIT_REASON and an exception?
>>     
>
> These are different cases. The exception is #MC in guest context,
> the EXIT_REASON is when a #MC happens while the CPU is executing
> the VM entry microcode.
>   

I see, thanks.

-- 
error compiling committee.c: too many arguments to function

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