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Re: [Xen-devel] [RFC] Hypercalls from HVM guests

To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Subject: Re: [Xen-devel] [RFC] Hypercalls from HVM guests
From: Steve Ofsthun <sofsthun@xxxxxxxxxxxxxxx>
Date: Fri, 07 Apr 2006 13:06:01 -0400
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Petersson, Mats wrote:

Interesting subject - I must have missed the September patchset... I've
been thinking a lot about para-virtualized drivers for HVM guests
(because it would improve performance on some functions by a great deal
to avoid intercepting half a dozen IO operations to actually perform a
single transaction - like one READ of the virtual hard-disk).

This is exactly our interest as well.

I'd like to make sure that you're aware that the AMD architecture also
has a VMMCALL instruction, which is opcode (0F 01 D9). It would be great
if you could implement some sort of auto-detect/switching so that your
code works for AMD too. Of course, we could intercept invalid opcode and
interpret the instruction, but that's far from a practical solution, I
would think.

Thanks for pointing that out.  I didn't realize the opcode was different.
I should be able to easily alter the hypercall page initialization to use
the proper AMD opcode.

What is the preferred method to distinguish SVM vs. VMX from within guest
code running in an HVM guest?

Steve Ofsthun - Virtual Iron Software, Inc.

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