Xen, IRQ-sharing and PCI passthrough

[Florian Wagner <f_wagner@syscomp.de>]

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Hello,

I've already sent this mail to the xen-users mailing list but haven't
gotten a useful answer. So excuse my double post.

I'm seeing problems with Xen and IRQ-sharing PCI cards which are passed
through to a Xen DomU. I'm not sure whether this is a problem with Xen
or with the Debian Xen Kernel (2.6.26-13 and newer from lenny) I'm
using. Judging from the single reply I got on xen-users I suspect the
former.

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 (sometimes resulting in destroyed filesystems).

Is there some other way to fix this than making sure the cards don't
share IRQs (which is quite a hassle when building a significant number
of machines with this configuration but with slightly different
hardware)? A fix from a newer Xen release we could backport to our
Debian kernel perhaps?


Regards
Florian

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

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

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