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Re: [Xen-devel] vmcs GUEST_CR0 unused?

  • To: Robert Phillips <rsp.vi.xen@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Thu, 01 Feb 2007 23:40:17 +0000
  • Delivery-date: Thu, 01 Feb 2007 15:40:09 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdGWlPIkkHQOLJNEduUNAAX8io7RQ==
  • Thread-topic: [Xen-devel] vmcs GUEST_CR0 unused?

On 1/2/07 21:49, "Robert Phillips" <rsp.vi.xen@xxxxxxxxx> wrote:

The same argument applies to hvm_vmx.cup_cr4 and GUEST_CR4.

Am I missing something?

Yes. GUEST_CR0 and GUEST_CR4 are the actual control-register values loaded into the processor when running in VMX context. This can be different from either the value the guest thinks it’s running with, and also different from the value loaded into the processor when running in root context (i.e., in Xen).  They are cached in software structures because it can save a vmread in some situations, which is worth around 50 cycles even on Core 2.

 -- Keir
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