On Fri, 13 Aug 2021 11:53:07 -0500 Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > [+cc Alex, kvm, linux-pci] > > On Fri, Aug 13, 2021 at 09:43:39AM +0200, Idar Lund wrote: > > Hi, > > > > I've been struggling with an error in linux since 5.11. Please find my bug > > report here: > > https://bugzilla.redhat.com/show_bug.cgi?id=1945565 > > > > Then I stumbled upon this mail thread: > > https://www.spinics.net/lists/linux-pci/msg102243.html which seems related. > > > > Is there another way to do this in 5.11+ or is this an unintentionally bug > > that got introduced in 5.11? > > Hi Idar, sorry for the trouble and thanks for the report! I cc'd some > VFIO experts who know more than I do about this. > > If I understand correctly, you have a PCI XHCI controller: > > pci 0000:06:00.0: [1b73:1100] type 00 class 0x0c0330 > xhci_hcd 0000:06:00.0: xHCI Host Controller > > and you want to unbind the xhci_hcd driver and bind vfio-pci instead: > > # echo '0000:06:00.0' > /sys/bus/pci/devices/0000\:06\:00.0/driver/unbind > # echo 0x1b73 0x1100 > /sys/bus/pci/drivers/vfio-pci/new_id > > In v5.10 (5.10.17-200.fc33.x86_64) this worked fine, but in v5.11 > (5.11.9-200.fc33.x86_64) the "new_id" write returns -EEXIST and > binding to vfio-pci fails. > > The patch you pointed out appeared in v5.11 as 3853f9123c18 ("PCI: > Avoid duplicate IDs in driver dynamic IDs list") [1], and I agree it > looks suspicious. There haven't been any significant changes to > pci-driver.c since then. > > Have you added "0x1b73 0x1100" to vfio-pci/new_id previously? I think > in v5.10, that would silently work (possibly adding duplicate entries > to the dynamic ID list) and every write to vfio-pci/new_id would make > vfio-pci try to bind to the device. > > In v5.11, if you write a duplicate ID to vfio-pci/new_id, you would > get -EEXIST and no attempt to bind. As far as I know, the dynamic ID > list is not visible in sysfs, so it might be hard to avoid writing a > duplicate. > > But if the vfio-pci dynamic ID list already contains "0x1b73 0x1100", > you should be able to ask vfio-pci to bind to the device like this: > > # echo 0000:06:00.0 > /sys/bus/pci/drivers/virtio-pci/bind > > I don't know if that's a solution, but would be useful to know whether > it's a workaround. [root@x1 vfio-pci]# echo 0x1b73 0x1100 > new_id [root@x1 vfio-pci]# echo 0x1b73 0x1100 > new_id bash: echo: write error: File exists [root@x1 vfio-pci]# uname -r 5.12.15-200.fc33.x86_64 Seems like it behaves as expected now. The new_id interface has some inherit issues, essentially all vfio-pci dynamic binding cases should instead be using the driver_override interface. The driverctl utility already makes use of this and will make your life a tiny bit easier. Thanks, Alex
