Re: [Xen-devel] MSI message data register configuration in Xen guests

[Rolu <rolu@xxxxxxxx>]

On Tue, Jun 26, 2012 at 4:38 AM, Deep Debroy <ddebroy@xxxxxxxxx> wrote:
> Hi, I was playing around with a MSI capable virtual device (so far
> submitted as patches only) in the upstream qemu tree but having
> trouble getting it to work on a Xen hvm guest. The device happens to
> be a QEMU implementation of VMWare's pvscsi controller. The device
> works fine in a Xen guest when I switch the device's code to force
> usage of legacy interrupts with upstream QEMU. With MSI based
> interrupts, the device works fine on a KVM guest but as stated before,
> not on a Xen guest. After digging a bit, it appears, the reason for
> the failure in Xen guests is that the MSI data register in the Xen
> guest ends up with a value of 4300 where the Deliver Mode value of 3
> happens to be reserved (per spec) and therefore illegal. The
> vmsi_deliver routine in Xen rejects MSI interrupts with such data as
> illegal (per expectation) causing all commands issued by the guest OS
> on the device to timeout.
>
> Given this above scenario, I was wondering if anyone can shed some
> light on how to debug this further for Xen. Something I would
> specifically like to know is where the MSI data register configuration
> actually happens. Is it done by some code specific to Xen and within
> the Xen codebase or it all done within QEMU?
>

This seems like the same issue I ran into, though in my case it is
with passed through physical devices. See
http://lists.xen.org/archives/html/xen-devel/2012-06/msg01423.html and
the older messages in that thread for more info on what's going on. No
fix yet but help debugging is very welcome.

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