[Xen-devel] Re: [RFC PATCH 18/33] Subarch support for CPUID instruction

[David Miller <davem@xxxxxxxxxxxxx>]

From: Zachary Amsden <zach@xxxxxxxxxx>
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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