From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: question on iommu _map_page
Date: Fri, 11 Jun 2010 09:32:50 +0100
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To: Kaushik Kumar Ram <kaushik@rice.edu>
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On 10/06/2010 22:59, "Kaushik Kumar Ram" <kaushik@rice.edu> wrote:

>> Actually I've implemented the better fix as xen-unstable:21476. Hope that
>> works okay for you.
> 
> 
> Checking if act->pin is zero before calling iommu_unmap_page() (in
> grant_table.c) is not sufficient since there can be multiple
> active grants all referring to the same mfn. In fact I came across iommu page
> faults because pages were
> getting unmapped from the IOMMU when active grants referring to these pages
> were still around.
> Ideally, there needs to be a per-page count of how many IOMMU mappings exists
> for a page. 
> I can't think of an obvious fix for this problem. For my purposes, I hacked
> page_info to add another counter which I guess is not an acceptable solution!

See if xen-unstable:21597 works for you.

 -- Keir