Re: [PATCH] Add MCE support to KVM

[Avi Kivity <avi@redhat.com>]

Gerd Hoffmann wrote:
> 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.  

Well, for true pv (not pv-on-hvm) it wouldn't use the MSR, would it?

> 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".

To different MSRs, or multiple writes to the same MSR?

>
> > 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?

It depends if the MSR may be considered global, or is required to be 
per-cpu.  Need to refresh my memory on this, but I remember reading this 
and saying 'yuck'.

-- 
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