On 8/27/25 16:33, Michael S. Tsirkin wrote:
> On Wed, Aug 27, 2025 at 03:52:05PM +0300, Dmitry Osipenko wrote:
>> On 8/27/25 11:12, Honglei Huang wrote:
>>> From: Honglei Huang <honglei1.hu...@amd.com>
>>>
>>> Commit 206cc44588f7 ("virtio: reject shm region if length is zero")
>>> enhanced the validation in virtio_get_shm_region() by adding a check
>>> for a zero-length shared memory region.
>>>
>>> It is performed before the underlying transport's .get_shm_region()
>>> implementation is called. This creates an issue in the virtio-gpu
>>> driver, where the `region` struct is part of a larger structure
>>> that is zero-initialized by drmm_kzalloc().
>>>
>>> Consequently, the `len` field is 0 at the time of the check, causing
>>> virtio_get_shm_region() to return false prematurely. This prevents the
>>> host visible memory feature from being enabled, even when the device
>>> supports it.
>>>
>>> To resolve this, this patch bypasses the inline helper and calls the
>>> underlying vdev->config->get_shm_region() function pointer directly.
>>> This ensures that the region's parameters are checked only after they
>>> have been populated by the transport, aligning with the intended logic.
>>>
>>> Signed-off-by: Honglei Huang <honglei1.hu...@amd.com>
>>> ---
>>> drivers/gpu/drm/virtio/virtgpu_kms.c | 6 ++++--
>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c
>>> b/drivers/gpu/drm/virtio/virtgpu_kms.c
>>> index 7dfb2006c561..ed5981248302 100644
>>> --- a/drivers/gpu/drm/virtio/virtgpu_kms.c
>>> +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
>>> @@ -174,8 +174,10 @@ int virtio_gpu_init(struct virtio_device *vdev, struct
>>> drm_device *dev)
>>> if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_RESOURCE_BLOB)) {
>>> vgdev->has_resource_blob = true;
>>> }
>>> - if (virtio_get_shm_region(vgdev->vdev, &vgdev->host_visible_region,
>>> - VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) {
>>> + if (vgdev->vdev->config->get_shm_region &&
>>> + vgdev->vdev->config->get_shm_region(
>>> + vgdev->vdev, &vgdev->host_visible_region,
>>> + VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) {
>>> if (!devm_request_mem_region(&vgdev->vdev->dev,
>>> vgdev->host_visible_region.addr,
>>> vgdev->host_visible_region.len,
>>
>> Hi, virtio_get_shm_region() change has been reverted by [1]. Don't think
>> anything else needs to be done.
>>
>> [1]
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20250827&id=ced17ee32a9988b8a260628e7c31a100d7dc082e
>>
>> +cc Michael Tsirkin
>>
>> Might be only good to send a stable kernel PR with that revert. I see
>> patch available only in linux-next, while stable kernels need to be
>> fixed sooner.
>
> sooner than what?
Next 6.17 kernel release. I see patch in the linux-next branch. Often
there is a -fixes branch for patches that go into RC kernel, but I don't
see one in your vhost kernel tree. Will the revert land into 6.17-rc4?
Everything is good if yes.
--
Best regards,
Dmitry
