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Re: [Xen-devel] question on iommu _map_page

To: Kaushik Kumar Ram <kaushik@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] question on iommu _map_page
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 27 May 2010 21:46:04 +0100
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Thread-topic: [Xen-devel] question on iommu _map_page
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It looks like the person who implemented that never needed the read-only
case. We need a function to map pages into the iommu read-only and to call
that from the grant code.

A patch to just call iommu_map_page() for any kind of grant mapping would be
acceptable for now, if you want to submit a patch.

 -- Keir

On 27/05/2010 21:37, "Kaushik Kumar Ram" <kaushik@xxxxxxxx> wrote:

> Hi all,
> I am trying to use the VT-d support with a PV driver domain which performs
> network I/O on behalf of guest domains.
> When I initiate any network I/O it results in I/O page faults. On taking a
> closer look I find that iommu_map_page() is called only for writable pages
> from __gnttab_map_grant_ref(). This results in page faults during packet
> transmission since pages are mapped read-only in this case.
> When I remove this restriction, I can get it working without any page faults.
> Is this a bug? or am I missing something here? I am using the latest unstable
> version of Xen. This part of the source code hasn't changed in a long time.
> Thanks!
> -Kaushik
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