Re: [Xen-devel] [PATCH] libxl: disallow PCI device assignment for HVM guest when PoD is enabled

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jan 10, 2014 at 12:28:52PM +0000, Jan Beulich wrote:
> >>> On 10.01.14 at 13:16, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 10/01/2014 11:46, Wei Liu wrote:
> >> On Fri, Jan 10, 2014 at 11:39:51AM +0000, Jan Beulich wrote:
> >>>>>> On 10.01.14 at 12:27, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> >>>> +    /* We cannot have PoD and PCI device assignment at the same time
> >>>> +     * for HVM guest. It was reported that VT-d engine cannot
> >>> There's still a "VT-d" left in here...
> >>>
> >> I mentioned AMD as well. Was trying to clarify things a bit more...
> > 
> > Use "IOMMU"/"PCI Passthrough"/etc as appropriate, which are vendor neutral.
> > 
> > There is no way for for PoD (or Paging for that matter) to work in
> > combination with PCIPassthrough, as you need all the backing RAM for all
> > gfns to exist to receive DMA.
> 
> That's going a little too far: If IOMMU faults were recoverable, dealing
> with non-present pages would become possible (with other caveats
> of course). So this is not a fundamental attribute of IOMMUs, but
> there doesn't seem to be any reason to believe that the current
> model would change any time soon for either of the vendors.
> 

Do you have suggestion on how this comment should be phrased?

Wei.

> Jan

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