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

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Message-ID: <20090317155555.GT11935@one.firstfloor.org>
Date:	Tue, 17 Mar 2009 16:55:55 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, "H. Peter Anvin" <hpa@...or.com>,
	Jan Beulich <jbeulich@...ell.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid

> well the choice fundamentally is
> 1) Have correct applications work, even though you might not always get
>    all new features that the hardware could have done.. at the expense
>    that someone who wants to do horrible things can
> 2) Have all latest features always there, but break correctly written
>    apps/oses every 2 years.

I'm not sure there will be that much breakage. It seems more like
a theoretical danger.

> 
> I'd go for option 1 any day of the week, hands down.
> Esp if the "cpu cloaking" kind of things really disable the
> instructions... but even without.

With cpu cloaking and disabling unknown instructions it would be fine
to go conservative.  But that's not what is being proposed.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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