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] treatment grant frames during save/restore

To: Jan Beulich <JBeulich@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] treatment grant frames during save/restore
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 27 May 2010 17:02:15 +0100
Cc:
Delivery-date: Thu, 27 May 2010 09:39:02 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4BFEAB750200007800004444@xxxxxxxxxxxxxxxxxx>
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>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acr9sVO/ORD6I+qlRw+IdarNt2T+JQABKW9A
Thread-topic: [Xen-devel] treatment grant frames during save/restore
User-agent: Microsoft-Entourage/12.24.0.100205
On 27/05/2010 16:27, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>> From what I can tell, grant frames get no special treatment by the tools
> during save, and hence get treated as normal memory during restore.
> If that's correct, it would seem that there's an accounting issue, since
> during restore a normal RAM page will be allocated by the tools for each
> grant frame, hence a domain that prior to save was below its limit
> could now end up crossing that limit, and thus unexpectedly fail to
> restore. If that's not a possibility, what am I missing?

Yes, it's an issue. Fixing is tricky since in some cases dom0 *wants* to be
able to map domU special Xen-heap pages. So we need to be able to specify
some kind of flag to say 'really map this domain's domain-heap RAM pages
only on this request' and preferably tunnel that flag through existing dom0
kernels so that it makes it unscathed down to the Xen hypercall. That's a
bit tricky I think, unless we do nasty things like steal bits from the
existing domid or pte.val fields to mmu_update(). Else we need dom0 kernel
mods too, which is a pain in the bum, but I suppose we could do that with
fallback to what we do currently.

 -- Keir

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



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