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

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Message-ID: <46EC1775.4000709@us.ibm.com>
Date:	Sat, 15 Sep 2007 12:33:41 -0500
From:	Anthony Liguori <aliguori@...ibm.com>
To:	Zachary Amsden <zach@...are.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>
Subject: Re: [kvm-devel] [PATCH] Refactor hypercall infrastructure

Zachary Amsden wrote:
> On Fri, 2007-09-14 at 16:44 -0500, Anthony Liguori wrote:
>
>   
>> So then each module creates a hypercall page using this magic MSR and 
>> the hypervisor has to keep track of it so that it can appropriately 
>> change the page on migration.  The page can only contain a single 
>> instruction or else it cannot be easily changed (or you have to be able 
>> to prevent the guest from being migrated while in the hypercall page).
>>
>> We're really talking about identical models.  Instead of an MSR, the #GP 
>> is what tells the hypervisor to update the instruction.  The nice thing 
>> about this is that you don't have to keep track of all the current 
>> hypercall page locations in the hypervisor.
>>     
>
> I agree, multiple hypercall pages is insane.  I was thinking more of a
> single hypercall page, fixed in place by the hypervisor, not the kernel.
>
> Then each module can read an MSR saying what VA the hypercall page is
> at, and the hypervisor can simply flip one page to switch architectures.
>   

That requires a memory hole though.  In KVM, we don't have a memory hole.

Regards,

Anthony Liguori

> Zach
>
>   

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