linux-kernel - Re: [kvm-devel] [PATCH] Refactor hypercall infrastructure

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Date:	Fri, 14 Sep 2007 16:46:30 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>
Subject: Re: [kvm-devel] [PATCH] Refactor hypercall infrastructure

Jeremy Fitzhardinge wrote:
> Anthony Liguori wrote:
>   
>> The whole point of using the instruction is to allow hypercalls to be
>> used in many locations.  This has the nice side effect of not
>> requiring a central hypercall initialization routine in the guest to
>> fetch the hypercall page.  A PV driver can be completely independent
>> of any other code provided that it restricts itself to it's hypercall
>> namespace.
>>     
>
> I see.  So you take the fault, disassemble the instruction, see that its
> another CPU's vmcall instruction, and then replace it with the current
> CPU's vmcall?
>   

Yup.

>> Xen is currently using 0/1/2.  I had thought it was only using 0/1. 
>> The intention was not to squash Xen's current CPUID usage so that it
>> would still be possible for Xen to make use of the guest code.  Can we
>> agree that Xen won't squash leaves 3/4 or is it not worth trying to be
>> compatible at this point?
>>     
>
> No, the point is that you're supposed to work out which hypervisor it is
> from the signature in leaf 0, and then the hypervisor can put anything
> it wants in the other leaves.
>   

Yeah, see, the initial goal was to make it possible to use the KVM 
paravirtualizations on other hypervisors.  However, I don't think this 
is really going to be possible in general so maybe it's better to just 
use leaf 0.  I'll let others chime in before sending a new patch.

Regards,

Anthony Liguori

>     J
>
>   

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