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RE: [Xen-devel] VP problematic for backend drivers on IA64?

To: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>, "Muli Ben-Yehuda" <mulix@xxxxxxxxx>
Subject: RE: [Xen-devel] VP problematic for backend drivers on IA64?
From: "Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>
Date: Tue, 24 Jan 2006 16:02:36 -0800
Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, okrieg@xxxxxxxxxx
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Thread-topic: [Xen-devel] VP problematic for backend drivers on IA64?
>translate the pfn to an mfn is sufficient

Actually, after thinking about this, it's a bit
more complicated because of the possibility that a DMA may
address more than one page.  If so, a simple DMA may need to be
translated into a scatter-gather (or a scatter-gather into
a more complex scatter-gather).

Not impossible, obviously because Xen/x86 handles this -- by
changing Linux, correct?

Do hardware IOMMU's in general handle this complication?
E.g. is there a cleanly defined interface that can be applied
to a VP domain "Xen IOMMU"?


> -----Original Message-----
> From: Ian Pratt [mailto:m+Ian.Pratt@xxxxxxxxxxxx] 
> Sent: Tuesday, January 24, 2006 4:43 PM
> To: Muli Ben-Yehuda; Magenheimer, Dan (HP Labs Fort Collins)
> Cc: xen-devel; okrieg@xxxxxxxxxx; ian.pratt@xxxxxxxxxxxx
> Subject: RE: [Xen-devel] VP problematic for backend drivers on IA64?
> > I understand that during the IA64 session at the summit there 
> > was some discussion on VP being problematic for the current 
> > backend drivers (or the other way around), and IOMMUs were 
> > suggested as a possible solution. Could you please elaborate 
> > on what's the problem?
> It's simply that the actual DMA operations need to use machine
> addresses. Ideally, you'd use an iommu to translate/partition, but in
> the absence of an iommu simply enabling a privileged domain 
> to read its
> p2m table and translate the pfn to an mfn is sufficient. 
> Ian

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