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

[Juergen Gross <jgross@xxxxxxxx>]

On 11/21/2014 03:54 PM, Jan Beulich wrote:
> > > > On 21.11.14 at 15:39, <JGross@xxxxxxxx> wrote:
> > 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's wrong with this large an address? 32-bit PV uses PAE, i.e.
> can map them. If the kernel isn't capable of that that's not
> something to make Xen (or the tools) refuse such assignments. I
> would only see an issue if a hypercall interface involved here isn't
> using wide enough fields (but these addresses should be read
> from the BARs, i.e. no hypercall involved).
The MFN format is part of the pv-ABI. And a MFN of a 32-bit pv-guest is
only 32 bits (even if don't take the invalid bit into account).

Should a pv-guest really be capable to map an address outside it's
accessible MFN-range?

Are the tools capable of processing such a mapping in case of saving the
domain?


Juergen

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