[Virtual ppce500] virtio_gpu virtio0: swiotlb buffer is full

Hello,

Just for info. The latest git kernel doesn't work with a virtio_gpu anymore.

QEMU command: qemu-system-ppc64 -M ppce500 -cpu e5500 -enable-kvm -m 
1024 -kernel uImage -drive 
format=raw,file=fienix-soar_3.0-2020608-net.img,index=0,if=virtio -nic 
user,model=e1000 -append "rw root=/dev/vda2" -device virtio-vga -device 
virtio-mouse-pci -device virtio-keyboard-pci -device pci-ohci,id=newusb 
-device usb-audio,bus=newusb.0 -smp 4

Error messages:

virtio_gpu virtio0: swiotlb buffer is full (sz: 4096 bytes), total 0 
(slots), used 0 (slots)
BUG: Kernel NULL pointer dereference on read at 0x00000010
Faulting instruction address: 0xc0000000000c7324
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K PREEMPT SMP NR_CPUS=4 QEMU e500
Modules linked in:
CPU: 2 PID: 1678 Comm: kworker/2:2 Not tainted 
5.9-a3_A-EON_X5000-11735-g06a81c1c7db9-dirty #1
Workqueue: events .virtio_gpu_dequeue_ctrl_func
NIP:  c0000000000c7324 LR: c0000000000c72e4 CTR: c000000000462930
REGS: c00000003dba75e0 TRAP: 0300   Not tainted 
(5.9-a3_A-EON_X5000-11735-g06a81c1c7db9-dirty)
MSR:  0000000090029000 <CE,EE,ME>  CR: 24002288  XER: 00000000
DEAR: 0000000000000010 ESR: 0000000000000000 IRQMASK: 0
GPR00: c0000000000c6188 c00000003dba7870 c0000000017f2300 c00000003d893010
GPR04: 0000000000000000 0000000000000001 0000000000000000 0000000000000000
GPR08: 0000000000000000 0000000000000000 0000000000000000 7f7f7f7f7f7f7f7f
GPR12: 0000000024002284 c00000003fff9200 c00000000008c3a0 c0000000061566c0
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR24: 0000000000000001 0000000000110000 0000000000000000 0000000000000000
GPR28: c00000003d893010 0000000000000000 0000000000000000 c00000003d893010
NIP [c0000000000c7324] .dma_direct_unmap_sg+0x4c/0xd8
LR [c0000000000c72e4] .dma_direct_unmap_sg+0xc/0xd8
Call Trace:
[c00000003dba7870] [c00000003dba7950] 0xc00000003dba7950 (unreliable)
[c00000003dba7920] [c0000000000c6188] .dma_unmap_sg_attrs+0x5c/0x98
[c00000003dba79d0] [c0000000005cd438] .drm_gem_shmem_free_object+0x98/0xcc
[c00000003dba7a50] [c0000000006af5b4] .virtio_gpu_cleanup_object+0xc8/0xd4
[c00000003dba7ad0] [c0000000006ad3bc] .virtio_gpu_cmd_unref_cb+0x1c/0x30
[c00000003dba7b40] [c0000000006adab8] 
.virtio_gpu_dequeue_ctrl_func+0x208/0x28c
[c00000003dba7c10] [c000000000086b70] .process_one_work+0x1a4/0x258
[c00000003dba7cb0] [c0000000000870f4] .worker_thread+0x214/0x284
[c00000003dba7d70] [c00000000008c4f0] .kthread+0x150/0x158
[c00000003dba7e20] [c00000000000082c] .ret_from_kernel_thread+0x58/0x60
Instruction dump:
f821ff51 7cb82b78 7cdb3378 4e000000 7cfa3b78 3bc00000 7f9ec000 41fc0014
382100b0 81810008 7d808120 48bc1ba8 <e93d0010> ebfc0248 833d0018 7fff4850
---[ end trace f28d194d9f0955a8 ]---

virtio_gpu virtio0: swiotlb buffer is full (sz: 4096 bytes), total 0 
(slots), used 0 (slots)
virtio_gpu virtio0: swiotlb buffer is full (sz: 16384 bytes), total 0 
(slots), used 0 (slots)

----

The kernel 5.8 works without any problems in this virtual machine.

Could you please check the latest updates?

Thanks,
Christian