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Re: [Xen-devel] dom0 kernel - irq nobody cared ... the continuing saga ..

>>> On 10.02.15 at 10:19, <linux@xxxxxxxxxxxxxx> wrote:
>> Coming back to the /proc/interrupts output you posted earlier:
>> /proc/interrupts shows the high count:
>>            CPU0       CPU1       CPU2       CPU3
>>   8:          0          0          0          0  xen-pirq-ioapic-edge  rtc0
>>   9:          1          0          0          0  xen-pirq-ioapic-level  acpi
>>  16:         29          0          0          0  xen-pirq-ioapic-level  
>> ehci_hcd:usb3
>>  18:     200000          0          0          0  xen-pirq-ioapic-level  
>> ata_generic
>> I would have thought that xen-pciback would install an interrupt
>> handler here too when a device using IRQ 18 gets handed to a
>> guest. May there be something broken in xen_pcibk_control_isr()?
> It seems to only do that for PV guests, not for HVM.

Interesting; no idea why that would be.

> Don't know how it wil go now after the bios update,
> lspci lists the SMBUS is also using irq 18 now, but it doesn't register
> a driver (according to lspci -k) and it doesn't appear in dom0's 
> /proc/interrupts.

With that I don't think you're going to have problems, as the IRQ
then is masked.

> How are things supposed to work with a machine with:
> - a shared irq
> - iommu + interrupt remapping enabled
> - HVM guests


> Would dom0 always see the legacy irq or is Xen or the iommu routing it 
> directly to 
> the guest ?

A shared IRQ can't be routed directly, as all involved domains need
to see it.

> And what would i suppose to see when using Xen's debug key 'i', should there 
> be an entry routing it to both guests ?

Yes, if both have a driver using it.

>. if you know some better way to figure out where the irq storm is 
> coming from or headed to .. i'm all ears (or eyes) ..

I suppose that's because there's no handler installed by pciback, yet
IRQs generated by the passed through device also arrive in Dom0,
and the driver for the device left in Dom0 doesn't claim the interrupts.


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