Date: Sun, 15 Mar 2009 17:09:45 -0700
From: Arjan van de Ven <arjan@infradead.org>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Jan Beulich <jbeulich@novell.com>,
       Xen-devel <xen-devel@lists.xensource.com>,
       Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
       the arch/x86 maintainers <x86@kernel.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid
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On Sun, 15 Mar 2009 17:05:26 -0700
Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> Arjan van de Ven wrote:
> > This is indicative of something that might be a huge bug in Xen:
> > Xen should never ever pass through CPUID bits it does not know.
> > If Xen does not honor that, there is a fundamental and eternally
> > recurring problem.... every time something new gets introduced Xen
> > likely breaks.
> 
> Yes, I'd agree; Xen should whitelist cpu capabilities rather than 
> blacklist them.  Jan expressed the opposite opinion (on the grounds
> that it precludes using features which don't require special OS or
> hypervisor support without Xen modifications).

Well.. pretty much all new instructions need Xen modifications due to
the need to be emulate to deal with traps/vmexits/etc right? 
So I don't quite see many cpuid bits that would NOT involve some Xen
modification or another ;)


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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