Xen users - Jun 2009 - AW: Xen, IRQ-sharing and PCI passthrough

Florian,

I read already here and there that you shall not use shared interrupts in
different PV DomUs,
although I never found a written statement. But behaviour is exactly as you
described, thus
I took care that cards that share an IRQ are in the same DomU/Dom0. I also
selected my
motherboards accordingly.

When I lately discussed lately with someone about MSI, I had the hope this could
help, because
in my system, one PCI slot shares IRQ with the PCIe x1 slots, so by enabling MSI
for the PCIe
slots, I was hoping to make the PCI slot usable to put it in some DomU. 

I never managed to try it out, though. I was able to enable MSI, but currently I
have an
old VGA card in the slot, the replacement would be an PCIe VGA that wants too
much power.

Anyhow, to proof the theory, please post dmesg | grep GSI, lspci, and cat
/proc/interrupts
of Dom0 and the used DomUs. But I think you can see on your own. Some
explanation is also
here (in German):

http://www.neobiker.de/wiki/index.php?title=XEN-PCI

BR,
Carsten.

----- Originalnachricht -----
Von: Florian Wagner <f_wagner@syscomp.de>
Gesendet: Fre, 26.6.2009 11:15
An: xen-users@lists.xensource.com
Betreff: [Xen-users] Xen, IRQ-sharing and PCI passthrough

Hello,

I''m seeing problems with Xen and IRQ-sharing PCI cards which are passed
through to a Xen DomU. As I''m not sure whether this is a problem with
Xen or with the Debian Xen Kernel (2.6.26-13 from lenny) I''m using,
I''d
like to ask here before posting a bug.

Reproducing the problem goes as follows:

 1. Put a PCI card in the machine and make sure it shares it''s IRQ with
another one. In my case it is a RIO Specialix card but I doubt this
makes any difference.

 2. Map the card to a domU and use it there. In the RIO case this
requires loading a kernel module and running a "rioboot" tool.

 3. Power down (either shutdown or destroy) the domU without stopping
the card (here: "riostop" and "rmmod rio").

The resulting kernel stack trace is as follows:

[  337.409057] pciback 0000:04:06.0: enabling device (0000 -> 0003)
[  337.480998] ACPI: PCI Interrupt 0000:04:06.0[A] -> Link [LNEA] -> GSI
19 (level, low) -> IRQ 19
[  361.759041] eth0: port 2(vif2.0) entering disabled state
[  361.845321] eth0: port 2(vif2.0) entering disabled state
[  362.462574] ACPI: PCI interrupt for device 0000:04:06.0 disabled
[  363.769836] irq 19: nobody cared (try booting with the "irqpoll"
option)
[  363.817174] Pid: 0, comm: swapper Not tainted 2.6.26-1-xen-amd64 #1
[  363.817174]
[  363.817174] Call Trace:
[  363.817174]  <IRQ>  [<ffffffff8037c9b0>]
irq_ignore_unhandled+0x1c/0x32
[  364.024802]  [<ffffffff8025f9ab>] __report_bad_irq+0x30/0x72
[  364.024802]  [<ffffffff8025fc74>] note_interrupt+0x287/0x2c7
[  364.024802]  [<ffffffff8026055c>] handle_level_irq+0xc3/0x118
[  364.024802]  [<ffffffff8020e13e>] do_IRQ+0x4e/0x9a
[  364.024802]  [<ffffffff8037d6c4>] evtchn_do_upcall+0x13c/0x1fc
[  364.024802]  [<ffffffff8020bbde>] do_hypervisor_callback+0x1e/0x30
[  364.024802]  <EOI>  [<ffffffff8037c992>]
force_evtchn_callback+0xa/0xb
[  364.024802]  [<ffffffff8020e795>] xen_safe_halt+0x90/0xa6
[  364.024802]  [<ffffffff8020a0c8>] xen_idle+0x2e/0x66
[  364.024802]  [<ffffffff80209cd6>] cpu_idle+0x97/0xb9
[  364.024802]
[  364.024802] handlers:
[  364.024802] [<ffffffffa00b42ad>] (megasas_isr+0x0/0x45 [megaraid_sas])
[  364.024802] Disabling IRQ #19

My take on this: Xen (or rather the dom0 kernel?) disables the shared
IRQ, which at that time is still in use by the other card. In my case
this crashes the machine, since the IRQ is shared with the RAID
controller.

So: Is it a kernel or a hypervisor bug? And should it be reported to the
Xen or the Debian maintainers?


Regards
Florian

------------------------------------------

Florian Wagner
Abteilung EDV
Telefon: 0821 / 4201 - 453
Fax: 0821 / 4201 - 411
E-Mail: f_wagner@syscomp.de

Syscomp Biochemische Dienstleistungen GmbH
August-Wessels-Straße 5, 86154 Augsburg
Postfach 102506, 86015 Augsburg
Telefon: 0821 / 4201 - 0
Fax: 0821 / 417992
Web: http://www.syscomp.de
E-Mail: syscomp@syscomp.de

Geschäftsführer:
  Dr. med. Bernd Schottdorf
  Gabriele Schottdorf

Registergericht Augsburg HRB 8670

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users