linux-kernel - Re: [PATCH] Add MCE support to KVM

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Date:	Tue, 21 Apr 2009 11:04:35 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...hat.com>
CC:	Huang Ying <ying.huang@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] Add MCE support to KVM

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Avi Kivity wrote:
>>>
>>> Then we would need to tell which read-only MSRs are setup writeable 
>>> and which aren't...
>>>
>>> I'm okay with an ioctl to setup MCE, but just make sure userspace 
>>> has all the information to know what the kernel can do rather than 
>>> the try-and-see-if-it-works approach.  We can publish this 
>>> information via KVM_CAP things, or via another ioctl (see 
>>> KVM_GET_SUPPORTED_CPUID2 for an example).
>>
>> Why not introduce a new exit type for MSR reads/writes that aren't 
>> handled by the kernel?  You just need a bit on the return that 
>> indicates whether to GPF because of an invalid MSR access.
>>
>> KVM_SET_MSRs should be reserved for MSRs that are performance 
>> sensitive.  Not all of them will be.
>>
>
> Right now everything in the vcpu is emulated in the kernel.  
> Everything else is emulated either in the kernel (irqchip) or in 
> userspace.  This makes things easier to understand, and is more future 
> friendly if more cpu features become virtualized by hardware.

Except cpuid, which is handled in userspace, sort of :-)  I think the 
same arguments apply here too.

Regards,

Anthony Liguori
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