Re: [PATCH] util: basic support for vendor-specific vfio drivers

On 8/4/22 2:36 PM, Jason Gunthorpe wrote: > On Thu, Aug 04, 2022 at 12:18:26PM -0600, Alex Williamson wrote: > > On Thu, 4 Aug 2022 13:51:20 -0300 > > Jason Gunthorpe <jgg(a)nvidia.com&gt; wrote: > > > > > On Mon, Aug 01, 2022 at 09:49:28AM -0600, Alex Williamson wrote: > > > > > > > > > > > Fortunately these new vendor/device-specific drivers can be easily > > > > > > > > identified as being "vfio-pci + extra stuff" - all that's needed is to > > > > > > > > look at the output of the "modinfo $driver_name" command to see if > > > > > > > > "vfio_pci" is in the alias list for the driver. > > > > > > We are moving in a direction on the kernel side to expose a sysfs > > > under the PCI device that definitively says it is VFIO enabled, eg > > > something like > > > > > > /sys/devices/pci0000:00/0000:00:1f.6/vfio/<N> > > > > > > Which is how every other subsystem in the kernel works. When this > > > lands libvirt can simply stat the vfio directory and confirm that the > > > device handle it is looking at is vfio enabled, for all things that > > > vfio support. > > > > > > My thinking had been to do the above work a bit later, but if libvirt > > > needs it right now then lets do it right away so we don't have to > > > worry about this hacky modprobe stuff down the road? > > > > That seems like a pretty long gap, there are vfio-pci variant drivers > > since v5.18 and this hasn't even been proposed for v6.0 (aka v5.20) > > midway through the merge window. We therefore have at least 3 kernels > > exposing devices in a way that libvirt can't make use of simply due to > > a driver matching test. > > That is reasonable, but I'd say those three kernels only have two > drivers and they both have vfio as a substring in their name - so the > simple thing of just substring searching 'vfio' would get us over that > gap. Looking at the aliases for exactly "vfio_pci" isn't that much more complicated, and "feels" a lot more reliable than just doing a substring search for "vfio" in the driver's name. (It would be, uh, .... "not smart" to name a driver "vfio<anything>" if it wasn't actually a vfio variant driver (or the opposite), but I could imagine it happening; :-/)