RE: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl

[Wathsala Wathawana Vithanage]

> > For cases where steering-tag is not required in user-space (VMMs),
> > caller asks the kernel to set steering-tag that corresponds the
> > cpu-id, cache-level, and PH combination at a given MSI-X vector entry
> > or ST table in config space. For such cases too, the kernel will read
> > the steering-tag from the _DSM and set the tag in the corresponding MSI-X or
> ST table entry.
> 
> We need to consider that there are vfio-pci variant drivers that support migration
> and make use of the vfio-pci-core feature interface.
> TPH programming appears to be very non-migration friendly, the attributes are
> very specific to the current host system.  Should migration and TPH be mutually
> exclusive?  This may be a factor in the decision to use a feature or ioctl.
> 

TPH isn't migration friendly at least for the time being. Therefore, this should be
implemented as an ioctl.

--wathsala