On 12/11/24 09:43, Vivek Kasireddy wrote: > If another driver for a VGA compatible GPU (that is passthrough'd) > locks the VGA resources (by calling vga_get()), then virtio_gpu > driver would encounter the following errors and fail to load during > probe and initialization: > > Invalid read at addr 0x7200005014, size 1, region '(null)', reason: rejected > Invalid write at addr 0x7200005014, size 1, region '(null)', reason: rejected > virtio_gpu virtio0: virtio: device uses modern interface but does not have VIRTIO_F_VERSION_1 > virtio_gpu virtio0: probe with driver virtio_gpu failed with error -22 > > This issue is only seen if virtio-gpu and the other GPU are on > different PCI buses, which can happen if the user includes an > additional PCIe port and associates the VGA compatible GPU with > it while launching Qemu: > qemu-system-x86_64... > -device virtio-vga,max_outputs=1,xres=1920,yres=1080,blob=true > -device pcie-root-port,id=pcie.1,bus=pcie.0,addr=1c.0,slot=1,chassis=1,multifunction=on > -device vfio-pci,host=03:00.0,bus=pcie.1,addr=00.0 ... > > In the above example, the device 03:00.0 is an Intel DG2 card and > this issue is seen when both i915 driver and virtio_gpu driver are > loading (or initializing) concurrently or when i915 is loaded first. > Note that during initalization, i915 driver does the following in > intel_vga_reset_io_mem(): > vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO); > outb(inb(VGA_MIS_R), VGA_MIS_W); > vga_put(pdev, VGA_RSRC_LEGACY_IO); > > Although, virtio-gpu might own the VGA resources initially, the > above call (in i915) to vga_get_uninterruptible() would result in > these resources being taken away, which means that virtio-gpu would > not be able to decode VGA anymore. This happens in __vga_tryget() > when it calls > pci_set_vga_state(conflict->pdev, false, pci_bits, flags); > where > pci_bits = PCI_COMMAND_MEMORY | PCI_COMMAND_IO > flags = PCI_VGA_STATE_CHANGE_DECODES | PCI_VGA_STATE_CHANGE_BRIDGE > > Therefore, to solve this issue, virtio-gpu driver needs to call > vga_get() whenever it needs to reclaim and access VGA resources, > which is during initial probe and setup. After that, a call to > vga_put() would release the lock to allow other VGA compatible > devices to access these shared VGA resources. > > Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> > Cc: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx> > Cc: Chia-I Wu <olvaffe@xxxxxxxxx> > Reported-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx> > --- > drivers/gpu/drm/virtio/virtgpu_drv.c | 40 +++++++++++++++++++++++++++- > 1 file changed, 39 insertions(+), 1 deletion(-) That fixed the problem, thanks! Applied to misc-next. -- Best regards, Dmitry
