Re: [Xen-devel] Issue with MSI in a HVM domU with several passed through PCI devices

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.06.12 at 22:57, Rolu <rolu@xxxxxxxx> wrote:
> I have a HVM domU running Ubuntu 12.04. It has several PCI devices
> passed through to it (USB controllers, onboard sound, ATI video card
> with gfx_passthru 0). It has some issues, the most apparent one with
> the sound, which doesn't play normally but repeats the same short
> fragment over and over for a while until moving on to the next
> fragment. The Xen dmesg prints lots of lines like:
> 
> (XEN) [2012-06-18 20:14:16] vmsi.c:108:d32767 Unsupported delivery mode 3

Which indicates something wrong in the guest kernel or in the
translation layers (qemu, less likely the hypervisor itself). Valid
MSIs can't have a delivery mode of 3 (a reserved encoding).

> The number behind 108:d varies occasionally.

Yes, that number is bogus (has no guaranteed relation to the
target domain).

> Since vmsi.c seems to deal with passing on MSI interrupts, I tried
> booting the domU with pci=nomsi. This made things work and sound now
> plays normally. Not using MSI at all doesn't seem like a very good
> solution though.
> 
> What makes this happen, and can I fix it in a better way?

Unless this is in the guest kernel, we'll likely need a code fix here,
but for determining what and where, we'd need you to provide
the qemu log for the domain as well (there ought to be entries
starting with "Update msi with pirq", and the gflags value is of
particular interest). Depending on what we see, we may then
need you to do some further debugging.

Jan


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