From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v3 for 4.5] x86/viridian: Freeze time reference counter when domain is paused Date: Tue, 21 Oct 2014 16:23:52 +0100 Message-ID: <1413905032.23337.51.camel@eu.citrix.com> References: <1413451271-47779-1-git-send-email-paul.durrant@citrix.com> <544696480200007800040BE8@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1XgbI6-0003xE-P4 for xen-devel@lists.xenproject.org; Tue, 21 Oct 2014 15:24:06 +0000 In-Reply-To: <544696480200007800040BE8@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Tim Deegan , Paul Durrant , Stefano Stabellini , xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org On Tue, 2014-10-21 at 16:22 +0100, Jan Beulich wrote: > >>> On 16.10.14 at 11:21, wrote: > > In XenServer system test it has become apparent that versions of Windows > > that make use of the time reference counter enlightenment cannot cope with > > large jumps forward in the value read from the MSR. Specifically, > > suspending a very large domain took approx. 45 minutes to complete and > > when the domain was resumed it was discovered that the WMI (Windows > > Management Instrumentation) service had hung. > > > > The reason a large jump forward is seen by the guest is that, when a guest > > is suspended, the guest stops running when the SCHEDOP_suspend hypercall is > > made, however the MSR value essentially keeps incrementing until the > > tool-stack issues DOMCTL_gethvmcontext. > > > > This patch adds code to freeze the value of the time reference counter > > on domain pause and 'thaw' it on domain unpause, but only thaw it if the > > domain is not shutting down. The absolute value of the counter is then > > saved in the viridian domain context record. This prevents the guest OS > > from experiencing large jumps in the value of the MSR and has been shown > > to reliably fix the problem with WMI. > > > > Signed-off-by: Paul Durrant > > ARM maintainers: I was about to commit this patch when I noticed > that there still was no ack from any of you for this (trivial) addition: Acked-by: Ian Campbell