On Mon, 11 Dec 2023 14:10:28 -0400 Jason Gunthorpe jgg@nvidia.com wrote:
On Mon, Dec 11, 2023 at 11:03:45AM -0700, Alex Williamson wrote:
On Sun, 26 Nov 2023 22:39:09 -0800 Yi Liu yi.l.liu@intel.com wrote:
the PF). Creating a virtual PASID capability in vfio-pci config space needs to find a hole to place it, but doing so may require device specific knowledge to avoid potential conflict with device specific registers like hiden bits in VF config space. It's simpler by moving this burden to the VMM instead of maintaining a quirk system in the kernel.
This feels a bit like an incomplete solution though and we might already posses device specific knowledge in the form of a variant driver. Should this feature structure include a flag + field that could serve to generically indicate to the VMM a location for implementing the PASID capability? The default core implementation might fill this only for PFs where clearly an emualted PASID capability can overlap the physical capability. Thanks,
In many ways I would perfer to solve this for good by having a way to learn a range of available config space - I liked the suggestion to use a DVSEC to mark empty space.
Yes, DVSEC is the most plausible option for the device itself to convey unused config space, but that requires hardware adoption so presumably we're going to need to fill the gaps with device specific code. That code might live in a variant driver or in the VMM. If we have faith that DVSEC is the way, it'd make sense for a variant driver to implement a virtual DVSEC to work out the QEMU implementation and set a precedent.
I mostly just want us to recognize that this feature structure also has the possibility to fill this gap and we're consciously passing it over and should maybe formally propose the DVSEC solution and reference it in the commit log or comments here to provide a complete picture. Thanks,
Alex