Re: [Xen-devel] [TESTDAY] PV / HVM pass-through works when IOMMU present; weird failures when not

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.06.13 at 18:10, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> Either way, if someone *is* passing through a device, it is probably a 
> security issue.

After looking around a bit, I'm convinced that the other day I must
have tried this with xm (for whatever reason) - libxl has at least
two issues here compared to xend/xm:

- Missing error handling: Errors for the domain creation case
  propagate all the way back up to domcreate_attach_pci(), at
  which point they get silently ignored. Without having looked
  deeper, my first suggestion would be to simply drop devices
  from the d_config->pcidevs[] and decrement
  d_config->num_pcidevs upon failure, thus skipping any
  respective backend setup.

- Not making use of xc_test_assign_device() (which would allow
  detecting the situation before _any_ other setup gets done for
  the device).

Of course it is all but helpful that the backend in qemu has no way
of verifying that the device is in fact owned by the guest, i.e. it
has to blindly set up things trusting that the information handed
to it is consistent.

Jan


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