[Xen-users] Xen, IRQ-sharing and PCI passthrough

[Florian Wagner <f_wagner@xxxxxxxxxx>]

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@xxxxxxxxxx

Syscomp Biochemische Dienstleistungen GmbH
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Postfach 102506, 86015 Augsburg
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Fax: 0821 / 417992
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E-Mail: syscomp@xxxxxxxxxx

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