Re: [Xen-devel] PCI-passthrough for 32 bit guests and high MMIO addresses

[Juergen Gross <jgross@xxxxxxxx>]

On 11/21/2014 03:45 PM, Andrew Cooper wrote:
> On 21/11/14 14:39, Juergen Gross wrote:
> > Hi,
> >
> > again a fallout from my "linear p2m list" tests:
> >
> > Trying to do PCI-passthrough with a 32-bit pv-domain I passed the
> > wrong device to the domain. The MMIO address was too large for a
> > MFN of a 32-bit system (it was 380003200000-3800036fffff).
> >
> > Instead of rejecting the operation Xen tried to perform it resulting
> > in a (quite understandable) failure in the domU.
> >
> > I think either the hypervisor or the tools should refuse to do
> > PCI-passthrough in this case.
> What actually goes wrong?  Does the 32bit guest truncate the MMIO region
> to 44 bits and try to map that?
I think it is 42 bits (the top 2 bits of the MFN are the "identity" and
"foreign" bits).

> I would completely agree that something (libxl?) should refuse this
> attempt to do passthrough, but I think pci-front should also kick up a
> fuss if it is able to detect this error.
Indeed.


Juergen

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