Re: [PATCH RFC] virtio-pci: share config interrupt between virtio devices

Sasha Levin
2014-09-21T13:47:51Z

On 09/21/2014 04:09 AM, Michael S. Tsirkin wrote:
>> The virtio 0.9.5 spec says that ISR is "unused" when in MSI-X mode. I
>> > don't think that you can depend on the device to set the configuration
>> > changed bit.
>> > The virtio 1.0 spec seems to have fixed that.
> Yes, virtio 0.9.5 has this bug. But in practice qemu always set this
> bit, so for qemu we could do that unconditionally. Pekka's lkvm tool
> doesn't unfortunately. It's easy to fix that, but it would be nicer to
> additionally probe for old versions of the tool, and disable IRQF_SHARED
> in that case.
>
> To complicate things, lkvm does not use a distinct subsystem vendor ID,
> in spite of the fact the virtio spec always required this explicitly.

I think I may be a bit confused here, but AFAIK we do set subsystem vendor
ID properly for our virtio-pci devices?

vpci->pci_hdr = (struct pci_device_header) {
.vendor_id = cpu_to_le16(PCI_VENDOR_ID_REDHAT_QUMRANET),
.device_id = cpu_to_le16(device_id),
[...]
.subsys_vendor_id = cpu_to_le16(PCI_SUBSYSTEM_VENDOR_ID_REDHAT_QUMRANET),

Thanks,
Sasha