Re: [PATCH] drm/virtio: Don't detach GEM from a non-created context

[Dmitry Osipenko]

On 7/7/26 22:01, Yiwei Zhang wrote:
> On Mon, Jun 29, 2026 at 2:39 PM Dmitry Osipenko
> <dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>>
>> Hi,
>>
>> On 6/25/26 20:08, Jason Macnak wrote:
>>> Applies the same treatment as commit 7cf6dd467e87 ("drm/virtio:
>>> Don't attach GEM to a non-created context in gem_object_open()")
>>> to virtio_gpu_gem_object_close() to avoid trying to detach
>>> a resource that was never attached due to a context
>>> never being created when context_init is supported.
>>>
>>> Fixes: 086b9f27f0ab ("drm/virtio: Don't create a context with default param if context_init is supported")
>>> Cc: <stable@xxxxxxxxxxxxxxx> # v6.14+
>>> Signed-off-by: Jason Macnak <natsu@xxxxxxxxxx>
>>> ---
>>>  drivers/gpu/drm/virtio/virtgpu_gem.c | 14 ++++++++------
>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_gem.c b/drivers/gpu/drm/virtio/virtgpu_gem.c
>>> index 435d37d36034..66c3f6f74e9c 100644
>>> --- a/drivers/gpu/drm/virtio/virtgpu_gem.c
>>> +++ b/drivers/gpu/drm/virtio/virtgpu_gem.c
>>> @@ -139,13 +139,15 @@ void virtio_gpu_gem_object_close(struct drm_gem_object *obj,
>>>       if (!vgdev->has_virgl_3d)
>>>               return;
>>>
>>> -     objs = virtio_gpu_array_alloc(1);
>>> -     if (!objs)
>>> -             return;
>>> -     virtio_gpu_array_add_obj(objs, obj);
>>> +     if (vfpriv->context_created) {
>>> +             objs = virtio_gpu_array_alloc(1);
>>> +             if (!objs)
>>> +                     return;
>>> +             virtio_gpu_array_add_obj(objs, obj);
>>>
>>> -     virtio_gpu_cmd_context_detach_resource(vgdev, vfpriv->ctx_id,
>>> -                                            objs);
>>> +             virtio_gpu_cmd_context_detach_resource(vgdev, vfpriv->ctx_id,
>>> +                                                    objs);
>>> +     }
>>>       virtio_gpu_notify(vgdev);
>>>  }
>>
>> The following scenario still will be troubling:
>>
>> 1. vgdev->has_context_init = true
>> 2. virtio_gpu_gem_object_open() invoked, GEM created and not attached to ctx
>> 3. virtio_gpu_context_init_ioctl() invoked, now vfpriv->context_created
>> = true
>> 4. virtio_gpu_gem_object_close() will detach resource that wasn't attached
>>
>> Add obj->ctx_attached member to struct virtio_gpu_object. See
>> virtio_gpu_object_attach() that uses obj->attached, do the same for
>> virtio_gpu_cmd_context_attach_resource().
>>
>> --
>> Best regards,
>> Dmitry
> 
> Hi Dmitry,
> 
> WIth context_init, resource attach/detach is per-context based. So a
> simple obj->ctx_attached won't work. One would have to track in the
> guest context_init ctx for whether a bo has been attached or not.
> 
> Another option is to accept this patch and live with the case you
> mentioned. We can consider that "invalid" user behavior.

Indeed, obj->ctx_attached shouldn't work for a shared/exported BO. Will
think on it for a couple days more and then merge this version if no
better ideas will appear.

-- 
Best regards,
Dmitry