linux-kernel - Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid

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Message-ID: <20090315170945.08344b86@infradead.org>
Date:	Sun, 15 Mar 2009 17:09:45 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Jan Beulich <jbeulich@...ell.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid

On Sun, 15 Mar 2009 17:05:26 -0700
Jeremy Fitzhardinge <jeremy@...p.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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