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Re: [Xen-devel] write_tsc in a PV domain?

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] write_tsc in a PV domain?
From: Chris Lalancette <clalance@xxxxxxxxxx>
Date: Thu, 27 Aug 2009 15:17:22 +0200
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Dan Magenheimer wrote:
>> Dan Magenheimer wrote:
>>> In that case, are you saying it is an illegal instruction for a PV
>>> guest to execute?  If so, we should not ignore it, we should fail
>>> the guest.  But that would be unfortunate for the RHEL5-64bit
>>> PV guests that actually DO use it.
>> Wait, what?  Could you point out where this is in RHEL-5 
>> 64-bit PV?  The only
>> case of write_tsc() I see in the code is in 
>> arch/i386/kernel/smpboot.c, which is
>> not used by the Xen PV implementation in RHEL-5.  Where else in the PV
>> implementation does a write_tsc?
> Hi Chris --
> I was surprised also, and digging deeper it looks like I was mistaken.
> I instrumented a hypervisor so that Xen would printk a console
> message if it was ignoring a wrmsr and was getting output
> when I launched a RHEL-5 PV guest.  But I refined the
> printk and it is NOT wrmsr(0x10) so you're right, it is
> NOT a write_tsc.
> Thanks for pointing out my error.

OK, cool, no problem.  I just wanted to make sure I wasn't missing something.

Chris Lalancette

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