On Mon, Dec 11, 2023 at 11:49:49AM -0700, Alex Williamson wrote: > On Mon, 11 Dec 2023 14:10:28 -0400 > Jason Gunthorpe <jgg@xxxxxxxxxx> 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@xxxxxxxxx> 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. How hard do you think it would be for the kernel to synthesize the dvsec if the varient driver can provide a range for it? On the other hand I'm not so keen on having variant drivers that are only doing this just to avoid a table in qemu :\ It seems like a reasonable thing to add to existing drivers, though none of them support PASID yet.. > 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. You mean by passing an explicit empty range or something in a feature IOCTL? Jason
