Re: xen_pciback: error enabling MSI-X / MSI for guest -- WAS: Re: Kernel panic when passing through 2 identical PCI devices

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.06.2025 13:10, J. Roeleveld wrote:
> On Monday, 23 June 2025 09:55:46 CEST Jan Beulich wrote:
>> On 21.06.2025 16:39, J. Roeleveld wrote:
>>> I managed to get past the kernel panic (sort of) by doing the following:
>>>
>>> 1) Ensure system is fully OFF before booting. A reset/reboot will cause
>>> these errors.
>>>
>>> 2) Fix the BIOS config to ensure the PCI-ports are split correctly. If
>>> anyone has a Supermicro board and gets errors about PCI-slots not getting
>>> full speed let me know.
>>>
>>> Not entirely convinced the 2nd was part of the cause, but that's ok.
>>>
>>> I now, however, get a new error message in the Domain0 dmesg:
>>> pciback <pci-address>: xen_map irq failed -28 for <domid> domain
>>> pciback <pci-address>: error enabling MSI-X for guest <domid>: err -28!
>>>
>>> For the NVMe devices, I get these twice, with the 2nd time complaining
>>> about MSI (without the -X)
>>>
>>> I feel there is something missing in my kernel-config and/or domain
>>> config.
>>> If anyone can point me at what needs to be enabled/disabled or suggestions
>>> on what I can try?
>>
>> The default number of extra IRQs the guest may (have) set up may be too
>> small. You may need to make use of Xen's extra_guest_irqs= command line
>> option.
> 
> I spent the entire weekend searching for possible causes/hints/things to try.
> That setting was one I had found some time ago (I think for MSI/MSI-X issues) 
> and it's currently set to:
> extra_guest_irqs=768,1024
> 
> Not sure if it makes sense to increase this further?

Seems unlikely, but you know how many interrupts the device(s) may have.

Jan