[Virtual ppce500] virtio_gpu virtio0: swiotlb buffer is full

Christian Zigotzky chzigotzky at xenosoft.de
Wed Aug 12 23:09:49 AEST 2020

Hello Daniel,

The VirtIO-GPU doesn't work anymore with the latest Git kernel in a 
virtual e5500 PPC64 QEMU machine [1,2] after the commit "drm/virtio: 
Call the right shmem helpers". [3]
The kernel 5.8 works with the VirtIO-GPU in this virtual machine.

I bisected today [4].

Result: drm/virtio: Call the right shmem helpers ( 
d323bb44e4d23802eb25d13de1f93f2335bd60d0) [3] is the first bad commit.

I was able to revert the first bad commit. [5] After that I compiled a 
new kernel again. Then I was able to boot Linux with this kernel in a 
virtual e5500 PPC64 QEMU machine with the VirtIO-GPU.

I created a patch. [6] With this patch I can use the VirtIO-GPU again.

Could you please check the first bad commit?


[1] 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

[2] 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]
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 
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] 
[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)



[4] https://forum.hyperion-entertainment.com/viewtopic.php?p=51377#p51377

[5] git revert d323bb44e4d23802eb25d13de1f93f2335bd60d0 //Output: 
[master 966950f724e4] Revert "drm/virtio: Call the right shmem helpers" 
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c 
index 6ccbd01cd888..346cef5ce251 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -150,7 +150,7 @@ static int virtio_gpu_object_shmem_init(struct 
virtio_gpu_device *vgdev,
      if (ret < 0)
          return -EINVAL;

-    shmem->pages = drm_gem_shmem_get_pages_sgt(&bo->base.base);
+    shmem->pages = drm_gem_shmem_get_sg_table(&bo->base.base);
      if (!shmem->pages) {
          return -EINVAL;

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