On Thu, 4 Aug 2022 13:51:20 -0300 Jason Gunthorpe <jgg@xxxxxxxxxx> 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. Libvirt needs backwards compatibility, so we'll need it to look for the vfio-pci driver through some long deprecation period. In the interim, it can look at module aliases, support for which will be necessary and might be leveraged for managed='yes' with variant drivers. Once vfio devices expose a chardev themselves, libvirt might order the tests as: a) vfio device chardev present b) driver is a vfio-pci modalias c) driver is vfio-pci The current state of the world though is that variant driver exist and libvirt can't make use of them. Thanks, Alex
