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Re: [Xen-devel] Hypercalls in Intel-VT
- To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>
- From: "Ashish Bijlani" <ashish.bijlani@xxxxxxxxx>
- Date: Sun, 28 Oct 2007 18:18:39 -0400
- Cc: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Mark Williamson <mark.williamson@xxxxxxxxxxxx>
- Delivery-date: Sun, 28 Oct 2007 15:19:18 -0700
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- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
does transition from non-root VMX mode to root VMX mode require GDT switch i.e. does GDT change from guest OS krnl's GDT to xen's GDT?
On 10/28/07,
Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx> wrote:
At 02:55 +0100 on 27 Oct (1193453721), Mark Williamson wrote: > Regarding the TLB flush, again, the hardware quite possibly does that. But > I'm not aware of anything in the VMX spec that exposes this detail, so Intel
> could easily tag the TLB entries as root / non-root to avoid flushing on a > VMEXIT / VMENTER. For all I know, they may do this already!
Right now, Intel processors always flush the whole TLB (including global
entries) on a transition to or from non-root mode. Newer AMD processors have tagged TLBs so you can do an exit/enter without flushing, but you have to explicitly discard the guest entries when it's appropriate. (Look
at arch/x86/hvm/svm/asid.c). That's on the road map for Intel too, I believe.
Cheers,
Tim.
-- Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508
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