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Date: Mon, 20 Apr 2009 09:52:49 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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To: Avi Kivity <avi@redhat.com>
CC: Anthony Liguori <anthony@codemonkey.ws>, Huang Ying <ying.huang@intel.com>,
       "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH] Add MCE support to KVM
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On 04/19/09 10:33, Avi Kivity wrote:
> Anthony Liguori wrote:
>> 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.

Yes, please.

> 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.
>
> While these are not compelling reasons, they at least lean the balance
> in favour of a kernel implementation.

The xen pv-on-hvm drivers use an msr to indicate "please place the 
hypercall page here".  Handling that in kernel isn't an option IMHO.

cheers,
   Gerd