On Thu, 4 Aug 2022 13:51:20 -0300 Jason Gunthorpe <jgg@nvidia.com> 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