linux-kernel - Re: [PATCH -v2] Add MCE support to KVM

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Message-ID: <49EDF057.9060501@codemonkey.ws>
Date:	Tue, 21 Apr 2009 11:12:07 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...hat.com>
CC:	Huang Ying <ying.huang@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v2] Add MCE support to KVM

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Huang Ying wrote:
>>> The related MSRs are emulated. MCE capability is exported via
>>> extension KVM_CAP_MCE and ioctl KVM_X86_GET_MCE_CAP_SUPPORTED. A new
>>> vcpu ioctl command KVM_X86_SETUP_MCE is used to setup MCE emulation
>>> such as the mcg_cap. MCE is injected via vcpu ioctl command
>>> KVM_X86_SET_MCE. Extended machine-check state (MCG_EXT_P) and CMCI are
>>> not simulated.
>>>   
>>
>> Maybe I'm missing something, but couldn't this be implemented 
>> entirely within userspace?  There's nothing VT/SVM specific about 
>> this.  If the issue is setting these MSRs from userspace via 
>> KVM_SET_MSRS isn't enough, perhaps we should add userspace MSR handling.
>>
>
> You also need to inject the MCE.

Regardless of the KVM interface for this, to go upstream to QEMU, this 
needs a TCG implementation which means the logic must be duplicated in 
userspace.  In particular, this is because a user-visible command is 
being introduced in the monitor.

So Avi, regardless of what interface is chosen for KVM, can you hold off 
applying these patches until there is a TCG implementation?  Otherwise, 
we'll be playing catchup between kvm-userspace and upstream QEMU forever.

Regards,

Anthony Liguori

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