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

[Deep Debroy <ddebroy@xxxxxxxxx>]

On Thu, Jun 28, 2012 at 1:52 PM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Jun 26, 2012 at 04:51:29AM +0200, Rolu wrote:
>> 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.
>
> Huh? You said in 
> http://lists.xen.org/archives/html/xen-devel/2012-06/msg01653.html
> "This worked!"

Hi Konrad, I believe Rolu's response in the thread you pointed to was
with respect to pass-through devices. This current thread is not about
pass-through devices but for a fully virtualized qemu device -
specifically a disk controller that is exposing raw-image backed files
from the host the guest as disks, very similar to the default LSI scsi
controller in qemu.

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