> From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > Sent: Friday, April 12, 2024 4:21 PM > > A userspace VMM is supposed to get the details of the device's PASID > capability > and assemble a virtual PASID capability in a proper offset in the virtual PCI > configuration space. While it is still an open on how to get the available > offsets. Devices may have hidden bits that are not in the PCI cap chain. For > now, there are two options to get the available offsets.[2] > > - Report the available offsets via ioctl. This requires device-specific logic > to provide available offsets. e.g., vfio-pci variant driver. Or may the device > provide the available offset by DVSEC. > - Store the available offsets in a static table in userspace VMM. VMM gets the > empty offsets from this table. > I'm not a fan of requesting a variant driver for every PASID-capable VF just for the purpose of reporting a free range in the PCI config space. It's easier to do that quirk in userspace. But I like Alex's original comment that at least for PF there is no reason to hide the offset. there could be a flag+field to communicate it. or if there will be a new variant VF driver for other purposes e.g. migration it can certainly fill the field too.
