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[Xen-devel] Re: Live migration fails due to c/s 20627

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>
Subject: [Xen-devel] Re: Live migration fails due to c/s 20627
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 15 Dec 2009 19:25:38 +0000
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>, "Dugger, Donald D" <donald.d.dugger@xxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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On 15/12/2009 18:25, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

> On 12/15/2009 09:24 AM, Xu, Dongxiao wrote:
>> If CPU has rdtsc but no rdtscp, then the VM exec control bit in VMCS
>> won't be turned on. Therefore if rdtscp instruction runs, it will encounter
>> invalid op code directly but no VMEXIT.
> Ah, right.  You'd need to make that particular illegal instruction vmexit.

We'd need to VMEXIT on any guest #UD and then call into our x86 emulator.
There's just a slight feeling that could have wider impact and implications
than the specific case we'd want to handle here. Then again, #UD is rare and
usually unexpected, so perhaps such a seemingly broad change is not so

 -- Keir

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