linux-kernel - Re: [RFC PATCH 18/33] Subarch support for CPUID instruction

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Message-Id: <20060718.134625.123974562.davem@davemloft.net>
Date:	Tue, 18 Jul 2006 13:46:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	zach@...are.com
Cc:	arjan@...radead.org, chrisw@...s-sol.org,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, jeremy@...p.org, ak@...e.de,
	akpm@...l.org, rusty@...tcorp.com.au, ian.pratt@...source.com,
	Christian.Limpach@...cam.ac.uk
Subject: Re: [RFC PATCH 18/33] Subarch support for CPUID instruction

From: Zachary Amsden <zach@...are.com>
Date: Tue, 18 Jul 2006 04:33:52 -0700

> You really need a CPUID hook.  The instruction is non-virtualizable, and 
> anything claiming to be a hypervisor really has to support masking and 
> flattening the cpuid namespace for the instruction itself.  It is used 
> in assembler code and very early in boot.  The alternative is injecting 
> a bunch of Xen-specific code to filter feature bits into the i386 layer, 
> which is both bad for Linux and bad for Xen - and was quite ugly in the 
> last set of Xen patches.

Userspace will still see the full set of cpuid bits, since
it can still execute cpuid unimpeded, is this ok?
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