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RE: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d

  • To: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Guy Zana" <guy@xxxxxxxxxxxx>
  • Date: Thu, 31 May 2007 14:00:01 -0400
  • Delivery-date: Thu, 31 May 2007 11:01:47 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acei7YJ0pr6pL1ntT2Wzdmq3YT+WeAABwdLMABRnVWAAGRV/QAAAghaw
  • Thread-topic: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d


> -----Original Message-----
> From: Kay, Allen M [mailto:allen.m.kay@xxxxxxxxx] 
> Sent: Thursday, May 31, 2007 8:44 PM
> To: Guy Zana; Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-devel] [VTD][patch 0/5] HVM device 
> assignment using vt-d
> >
> >Just FYI.
> >
> >Neocleus' pass-through patches performs the "change polarity" trick.
> >With changing the polarity, our motivation was to reflect 
> the allocated 
> >device's assertion state to the HVM AS IS.
> >
> >Regarding the performance, using a USB 2.0 storage device 
> (working with 
> >DMA), a huge file copy was compared when working in 
> pass-through, and 
> >when working in native (on the same OS), the time differences were 
> >negligible so I'm not sure yet about the impact of doubling 
> the number 
> >of interrupts. The advantage of changing the polarity is the 
> >simplicity.
> >
> >Anyways, We'll release some patches during the day so you could give 
> >your comments.
> >
> >Thanks,
> >Guy.
> >
> How do you handle DMA buffers without hardware support?  Did 
> you modify the device driver in HVM to get the machine 
> physical address?

We actually launch a HVM domain with its P2M table populated in a 1:1 fashion 
(where the gpfn==mfn), 
We gave a lecture at the last Xen Summit, you can see it at:

The 1:1 layout is still not robust as we would like it to be, it doesn't 
support domain recreation for instance.

> Once your patch is released, I will take a look at it.



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