[Xen-devel] PCI passthrough hotplugging with stubdom: create new mem mapping failed!

[HW42 <hw42@xxxxxxxxx>]

Hi,

I'm currently debugging why hotplugging pci devices doesn't work with the
linux based stubdom used in the next Qubes release (based on Anthony's
and Eric's patches).

When attaching a pci device to a running domain qemu in the stubdom
throws the following error:

  [00:06.0] xen_pt_region_update: Error: create new mem mapping failed! (err: 1)

It seems that the problem is that do_pci_add first triggers the qemu
device_add command (via xenstore or qmp) and then calls
xc_domain_iomem_permission. So when qemu calls xc_domain_memory_mapping
during the setup of the device it fails because the permissions aren't
configured yet.

When I just move the qemu device_add further down it indeed works.

This problem does not appear when running qemu in dom0. Probably because
dom0 has anyway permission to call xc_domain_memory_mapping.

I don't understand why this is not a problem for minios based stubdoms.
Maybe just timing?

Does the above analysis sounds correct? (I'm not really familiar with
this). If yes, where exactly should the qemu pci_add be moved?

Thanks.

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