From: Alex Williamson<alex.williamson@xxxxxxxxxx>Currently the PASID cap is enabled by default when a device is probed
Sent: Thursday, May 11, 2023 1:25 AM
On Tue, 9 May 2023 08:34:53 +0000
"Tian, Kevin"<kevin.tian@xxxxxxxxx> wrote:
According to PCIe spec (7.8.9 PASID Extended Capability Structure):Backup for a moment, VFs are governed by the PASID capability on the
The PASID configuration of the single non-VF Function representing
the device is also used by all VFs in the device. A PF is permitted
to implement the PASID capability, but VFs must not implement it.
To enable PASID on VF then one open is where to locate the PASID
capability in VF's vconfig space. vfio-pci doesn't know which offset
may contain VF specific config registers. Finding such offset must
come from a device specific knowledge.
PF. The PASID capability exposes control registers that imply the
ability to manage various feature enable bits. The VF owner does not
have privileges to manipulate those bits. For example, the PASID Enable
bit should restrict the endpoint from sending TLPs with a PASID prefix,
but this can only be changed at the PF level for all associated VFs.
The protocol specified in 7.8.9.3 defines this enable bit as RW. How do
we virtualize that? Either it's virtualized to be read-only and we
violate the spec or we allow it to be read-write and it has no effect,
which violates the spec.
by iommu driver. Leaving it enabled in PF while guest wants it disabled
in VF is harmless. W/o proper setup in iommu side the VF cannot
do real work with PASID.