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Re: [Xen-devel] Re: [PATCH] x86/pvclock-xen: zero last_value on resume

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Glauber Costa <glommer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] x86/pvclock-xen: zero last_value on resume
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Wed, 27 Oct 2010 13:59:54 -0700
Cc: "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, kvm-devel <kvm@xxxxxxxxxxxxxxx>, Eelco Dolstra <e.dolstra@xxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Olivier Hanesse <olivier.hanesse@xxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>
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I'll check it this evening when I'm at a working network again :(

"Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

> On 10/26/2010 10:48 AM, Glauber Costa wrote:
>> On Tue, 2010-10-26 at 09:59 -0700, Jeremy Fitzhardinge wrote:
>>> If the guest domain has been suspend/resumed or migrated, then the
>>> system clock backing the pvclock clocksource may revert to a smaller
>>> value (ie, can be non-monotonic across the migration/save-restore).
>>> Make sure we zero last_value in that case so that the domain
>>> continues to see clock updates.
>>> [ I don't know if kvm needs an analogous fix or not. ]
>> After migration, save/restore, etc, we issue an ioctl where we tell
>> the host the last clock value. That (in theory) guarantees
>> I am not opposed to this patch in any way, however.
>HPA, do you want to take this, or shall I send it on?
>    J

Sent from my mobile phone.  Please pardon any lack of formatting.

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