Re: [Qemu-devel] [Xen-devel] [PATCH v2] xen/pt: Fix a xen passthrough failure

[Zhao Yan]

hi Andrew,

It's a pci device that does not support legacy intx mode, but it accidently
reports PCI_INTERRUPT_PIN as 1, which should be 0 instead.
So, in dom0, the machine irq is 0, which will cause later
xc_physdev_map_pirq() fail and passthrough failure.

Therefore, we treat this case as PCI_INTERRUPT_PIN is 0 and report to guest
the right value (0) of PCI_INTERRUPT_PIN.
Then in guest, it's able to use msi mode and function normally.

On Mon, Dec 03, 2018 at 02:12:58PM +0000, Andrew Cooper wrote:
> On 03/12/2018 05:04, Zhao Yan wrote:
> > For some pci device, even its PCI_INTERRUPT_PIN is not 0, it actually
> > doesn't support INTx mode, so its machine irq read from host sysfs is 0.
> > In that case, report PCI_INTERRUPT_PIN as 0 to guest and let passthrough
> > continue.
> 
> What causes this problem?  It it a non-PCI compliant device?  Is it a
> device which has legacy lines prohibited?
> 
> ~Andrew