Re: [v2 1/3] virtio-gpu: Add support for VIRTIO_GPU_BLOB_FLAG_USE_USERPTR flag

[Honglei Huang <honghuan@amd.com>]

On 2025/11/21 13:28, Akihiko Odaki wrote:
> On 2025/11/21 14:21, Honglei Huang wrote:
>>
>>
>> On 2025/11/21 11:39, Akihiko Odaki wrote:
>>> On 2025/11/21 12:14, Honglei Huang wrote:
>>>>
>>>>
>>>> On 2025/11/21 10:56, Akihiko Odaki wrote:
>>>>> On 2025/11/21 11:47, Honglei Huang wrote:
>>>>>> Add support for the USE_USERPTR blob flag in virtio-gpu to enable
>>>>>> user pointer mapping for blob resources. This allows guest 
>>>>>> applications
>>>>>> to use user-allocated memory for GPU resources more efficiently.
>>>>>>
>>>>>> Changes include:
>>>>>> - Add VIRTIO_GPU_BLOB_FLAG_USE_USERPTR flag definition
>>>>>> - Enhance blob resource creation to handle userptr flag properly
>>>>>> - Remove arbitrary nr_entries limit (16384) in mapping creation
>>>>>> - Add conditional handling for userptr vs regular blob mapping
>>>>>
>>>>> I don't see the added conditional handling.
>>>>
>>>> Sorry, the additional handing is replaced by the fixing of value check.
>>>> I will correct this commit message in the next version.
>>>
>>> Not just the commit message, but it also questions the utility of 
>>> VIRTIO_GPU_BLOB_FLAG_USE_USERPTR and VIRTIO_GPU_F_RESOURCE_USERPTR. 
>>> Neither of them adds a new functionality. They should be dropped if 
>>> they are also replaced with the fix.
>>>
>>
>> Yes totally agreed, it is my mistaken, I shouldn't mix the code for 
>> fixing and the code for adding new features in one submission.
>>
>> Actually this patch set are for another components upstream test, for 
>> the sake of convenience, I have added both the fix and feature here,
>> that is a bad idea.
>>
>> Will split the fix part into previous thread.
>>
>> And for the check value fix thread, will send v4 as the final version.
> 
> Splitting fixes and features is a good idea, but that's not what I meant.
> 
> What I pointed out is that, it seems that one of the "features" you are 
> adding, namely VIRTIO_GPU_F_RESOURCE_USERPTR does nothing at at all. So 
> I'm wondering if you forgot to add a real implementation or the feature 
> is just no longer necessary.

Understood, actually the resource of flag VIRTIO_GPU_F_RESOURCE_USERPTR 
just reuses the feature of VIRTIO_GPU_BLOB_MEM_GUEST: using the 
virtio_gpu_create_mapping_iov function to map the iov from guest.

In qemu, the handing of VIRTIO_GPU_F_RESOURCE_USERPTR and 
VIRTIO_GPU_BLOB_MEM_GUEST basically same.

The VIRTIO_GPU_F_RESOURCE_USERPTR is from guest userspace, but the
VIRTIO_GPU_BLOB_MEM_GUEST comes from guest kernel.
So in VIRTIO kernel and virglrenderer they are different, see VIRTIO 
kerenl: [1], and virglrenderer: [2].

May I need to change the organizational form of this patch set?

[1]: 
https://lore.kernel.org/lkml/20251112074548.3718563-1-honglei1.huang@amd.com/
[2]: 
https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1568/diffs#14086999aaf57fc68a3d7d639ab280c3a2672430:~:text=if%20(args%2D%3Eblob_flags%20%26%20VIRGL_RENDERER_BLOB_FLAG_USE_USERPTR)%20%7B