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

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Date:	Mon, 20 Apr 2009 10:59:51 +0200
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Anthony Liguori <anthony@...emonkey.ws>,
	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

On 04/20/09 10:26, Avi Kivity wrote:
> Gerd Hoffmann wrote:
>> 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.
>
> The contents of the hypercall page are vendor specific. This can be
> handled from userspace (though ideally we'd abstract the cpu vendor
> away).

Well, xenner doesn't do vmcalls, so the page isn't vendor specific.  It 
looks different for 32bit / 64bit guests though.  And it actually can be 
multiple pages (with one msr write per page).  So the interface for 
in-kernel handling would be more complex than "here is a hypercall page 
for you".

 > The Hyper-V hypercall page is more problematic, as it's specified to 
 > be an overlay; the page doesn't have to exist in guest RAM.

In userspace it should be easy to handle though as qemu can just create 
a new memory slot, right?

cheers,
   Gerd
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