WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] Live migration with MMIO pages

To: Keir Fraser <keir@xxxxxxxxxxxxx>, Kieran Mansley <kmansley@xxxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Live migration with MMIO pages
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 02 Nov 2007 10:51:25 +0000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 02 Nov 2007 03:52:11 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <C350AF7F.17D36%keir@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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcgdPQOPQfBScIkwEdyrMQAX8io7RQAAUyZO
Thread-topic: [Xen-devel] Live migration with MMIO pages
User-agent: Microsoft-Entourage/11.3.6.070618
On 2/11/07 10:42, "Keir Fraser" <keir@xxxxxxxxxxxxx> wrote:

> I also note that guarding the mark-dirty-or-zap-writable-bit with
> mfn_valid() is not really correct. mfn_valid() only checks whether the mfn <
> max_page. I bet this would not work if you migrate on a machine with 4GB of
> RAM, as the MMIO hole will be below max_page. Really mfn_valid needs to
> handle such MMIO holes, or the shadow code needs to be using a test other
> than mfn_valid in many places (e.g., the function iomem_page_test() that you
> added before).

Actually Tim reckons that use of mfn_valid() is okay because although you
will lose the _PAGE_RW bit on your mmio mapping temporarily, if the mmio mfn
is less than max_page, you've fixed up the fault path now so that you should
get the _PAGE_RW bit back again when the guest attempts a write access.

However, we think that the !mfn_valid() test that gates adding
_PAGE_PAT|PAGE_PCD|_PAGE_PWT to the passthru flags should go away. We'll
already have validated those flags even for ordinary RAM mappings for a PV
guest, and there are cases where cache attributes have to be different for
RAM pages. So probably the test should unconditionally pass through those
flags if the domain is !shadow_mode_refcounts.

 -- Keir




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel