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

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Message-ID: <97D612E30E1F88419025B06CB4CF1BE10379ED0A@scsmsx412.amr.corp.intel.com>
Date:	Fri, 14 Sep 2007 17:10:03 -0700
From:	"Nakajima, Jun" <jun.nakajima@...el.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Anthony Liguori" <anthony@...emonkey.ws>,
	<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:
> Nakajima, Jun wrote:
> > > > one.  Start the kvm leaves at 0x40001000 or something?
> > > > 
> > > > 
> > > Yeah, that works with me.
> > > 
> > 
> > To me this is the beginning of fragmentation. Why do we need
different
> > and VMM-specific Linux paravirtualization for hardware-assisted
> > virtualization? That would not be good for Linux.
> > 
> 
> On the contrary.  Xen already has a hypercall interface, and we need
to
> keep supporting it.  If we were to also support a vmm-independent
> interface (aka "kvm interface"), then we need to be able to do that in
> parallel.  If we have a cpuid leaf clash, then its impossible to do
so;
> if we define the new interface to be disjoint from other current users
> of cpuid, then we can support them concurrently.
> 
>     J

Today, 3 CPUID leaves starting from 0x4000_0000 are defined in a generic
fashion (hypervisor detection, version, and hypercall page), and those
are the ones used by Xen today. We should extend those leaves (e.g.
starting from 0x4000_0003) for the vmm-independent features as well.

If Xen needs additional Xen-specific features, we need to allocate some
leaves for those (e.g. 0x4000_1000)

Jun
---
Intel Open Source Technology Center
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