Hi,
any comment?
Thanks,
Laurent
Le 20/12/2020 à 17:35, Laurent Vivier a écrit :
> In the kernel, virtio_gpu_init() uses virtio_get_shm_region()
> since
> commit 6076a9711dc5 ("drm/virtio: implement blob resources: probe for host
> visible region")
> but vm_get_shm_region() unconditionally uses VIRTIO_MMIO_SHM_SEL to
> get the address and the length of the region.
>
> commit 38e895487afc ("virtio: Implement get_shm_region for MMIO transport"
>
> As this is not implemented in QEMU, address and length are 0 and passed
> as is to devm_request_mem_region() that triggers a crash:
>
> [drm:virtio_gpu_init] *ERROR* Could not reserve host visible region
> Unable to handle kernel NULL pointer dereference at virtual address (ptrval)
>
> According to the comments in the kernel, a non existent shared region
> has a length of (u64)-1.
>
> This is what we return now with this patch to disable the region.
>
> Signed-off-by: Laurent Vivier <laur...@vivier.eu>
> ---
> hw/virtio/virtio-mmio.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
> index e1b5c3b81e37..610661d6a526 100644
> --- a/hw/virtio/virtio-mmio.c
> +++ b/hw/virtio/virtio-mmio.c
> @@ -191,6 +191,14 @@ static uint64_t virtio_mmio_read(void *opaque, hwaddr
> offset, unsigned size)
> return 0;
> }
> return vdev->generation;
> + case VIRTIO_MMIO_SHM_LEN_LOW:
> + case VIRTIO_MMIO_SHM_LEN_HIGH:
> + /*
> + * VIRTIO_MMIO_SHM_SEL is unimplemented
> + * according to the linux driver, if region length is -1
> + * the shared memory doesn't exist
> + */
> + return -1;
> case VIRTIO_MMIO_DEVICE_FEATURES_SEL:
> case VIRTIO_MMIO_DRIVER_FEATURES:
> case VIRTIO_MMIO_DRIVER_FEATURES_SEL:
>
