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

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Message-ID: <f73f7ab80904192057q3d918ceco81c09febb493e1c3@mail.gmail.com>
Date:	Sun, 19 Apr 2009 23:57:18 -0400
From:	Kyle Moffett <kyle@...fetthome.net>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Avi Kivity <avi@...hat.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 -v2] Add MCE support to KVM

On Sun, Apr 19, 2009 at 9:19 PM, Huang Ying <ying.huang@...el.com> wrote:
> On Sat, 2009-04-18 at 23:54 +0800, 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.
>>
>> Also, if you implement the MSR logic in userspace, it's pretty simple to
>> make it work in the non-TCG case which will be a requirement for
>> upstream merging.
>
> There is more logic than just KVM_SET_MSRS, such as BANK reporting
> disabling, overwriting rules, triple fault for UC MCE during MCIP.
> Although these logic can be implemented in user space, I think put them
> in kernel space is easy to be understood. And the code is pretty short.

IMO the main reason to put this in kernel-space would be to make it
possible to automatically forward some MCE errors generated by the
real hardware (RAM ECC errors for example) down into the VM.  Right
now I suppose you could do that with the patches to forward RAM-based
hard MCEs to userspace using SIGSEGV and handling the SIGSEGV in
userspace, but that seems more fragile to me.

Cheers,
Kyle Moffett
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