This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


RE: [Xen-devel] Error restoring DomU when using GPLPV

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Error restoring DomU when using GPLPV
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Tue, 4 Aug 2009 20:39:46 +1000
Cc: Joshua West <jwest@xxxxxxxxxxxx>
Delivery-date: Tue, 04 Aug 2009 03:40:16 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <C69DBD9A.1143B%keir.fraser@xxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <AEC6C66638C05B468B556EA548C1A77D016DE058@trantor> <C69DBD9A.1143B%keir.fraser@xxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-topic: [Xen-devel] Error restoring DomU when using GPLPV
> Could the grant-table/shinfo Xenheap pages be confusing matters I
> The save process may save those pages out - since dom0 can map them it
> also save them - and then they get mistakenly restored as domheap
pages at
> the far end. All would work out okay in the end when you remap those
> pages during GPLPV restore as the domheap pages would get implciitly
> But maybe there is not allocation headroom for the guest in the
meantime so
> the restore fails.
> Just a theory. Maybe you could try unmapping grant/shinfo pages in the
> suspend callback? This may not help for live migration though, where
> get transmitted before the callback. It may be necessary to allow dom0
> specify 'map me a page but not if it's special' and plumb that up to
> xc_domain_save. It'd be good to have the theory proved first.

I took the easier path and told my grant code to map 2 less pages, and
sure enough it tries to allocate 31 pages (which succeeds) but then
tries to allocate 7 (which fails). So the 31 (was 33) must contain the
grant table pages etc. I'll attempt to add the unmap code you requested
and see if it makes a difference...

So why doesn't PV have this problem? Does it not send the pages first?
And do you think that a Linux HVM domain with PV drivers would suffer
the same fate?



Xen-devel mailing list