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

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Message-Id: <49BE6D50.76E4.0078.0@novell.com>
Date:	Mon, 16 Mar 2009 14:16:32 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	"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>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid

>>> Arjan van de Ven <arjan@...radead.org> 16.03.09 01:09 >>>
>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 ;)

No, new (user-mode accessible) instructions represent precisely the kind
of extension that do not require hypervisor (or OS) awareness (see SSE2
etc, AES, FMA). New registers otoh are examples of where awareness is
needed (SSE, AVX), as would be new privileged instructions.

Jan

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