Re: [PATCH 1/2] drm/amdkfd: Get foreign dma-buf info

["Chen, Xiaogang" <xiaogang.chen@amd.com>]

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On 10/27/2026 4:02 AM, Christian König wrote:
>
> On 10/23/26 16:48, Xiaogang.Chen wrote:
>> From: Xiaogang Chen<xiaogang.chen@amd.com>
>>
>> When import a dma-buf into kfd driver the dma-buf can be exported from amdgpu
>> driver or another driver/component(foreign).
>>
>> Current kfd driver can't handle foreign dma-buf at AMDKFD_IOC_GET_DMABUF_INFO.
>> When a foreign dma-buf is imported into kfd driver(ex udmabuf) it becomes a
>> normal kfd buf that can be exported, then imported in same or another amdgpu
>> device. That requires kfd drive to get new exported dma-buf info before it is
>> imported.
> Yeah again absolutely clear NAK to that!
>
> Re-exporting the imported DMA-buf this way is *clearly* not allowed!
This "Re-exporting" is from driver point view. App exports only once. 
The original buf was generated by Thunk using foreign driver/component 
exported buf when app allocates buf. Driver sees "exporting the imported 
DMA-buf", app does not. App uses same routine to handle it as for normal 
kfd buf.
>
> What you can do is to re-export the original DMA-buf so that you get the same fd you would get from the original exporter.
>
> In other words you can then also ask the original exporter for that information.

During the procedure there is only one dma-buf instance which was 
generated by foreign driver/component. kfd does not generate new dma-buf 
instance. It saves this dma-buf instance. kfd generates a "struct 
kgd_mem" to wrap this dma-buf instance and record its metadata. Then 
dma-buf info is obtained from this "struct kgd_mem".

Regards

Xiaogang

>
> Regards,
> Christian.
>
>> Extend kfd_ioctl_get_dmabuf_info to handle args->dmabuf_fd that was originally
>> exported by foreign component.
>>
>> Signed-off-by: Xiaogang Chen<xiaogang.chen@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h    |  3 ++
>>   .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  | 47 +++++++++++++++++++
>>   drivers/gpu/drm/amd/amdkfd/kfd_chardev.c      | 11 ++++-
>>   3 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>> index e3da382ceb3c..170f0ea0b78a 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>> @@ -347,6 +347,9 @@ int amdgpu_amdkfd_gpuvm_import_dmabuf_fd(struct amdgpu_device *adev, int fd,
>>   					 uint64_t va, void *drm_priv,
>>   					 struct kgd_mem **mem, uint64_t *size,
>>   					 uint64_t *mmap_offset);
>> +int amdgpu_amdkfd_gpuvm_imported_dmabuf_info(void *kgd_info, int fd,
>> +					     uint64_t *size, uint32_t *flags,
>> +					     uint32_t *gpu_id);
>>   int amdgpu_amdkfd_gpuvm_export_dmabuf(struct kgd_mem *mem,
>>   				      struct dma_buf **dmabuf);
>>   void amdgpu_amdkfd_debug_mem_fence(struct amdgpu_device *adev);
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> index a5d1d83ee5d3..b7fea3a2f5ca 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> @@ -2452,6 +2452,53 @@ static int import_obj_create(struct amdgpu_device *adev,
>>   	return ret;
>>   }
>>   
>> +int amdgpu_amdkfd_gpuvm_imported_dmabuf_info(void *kgd_info, int fd,
>> +					     uint64_t *size, uint32_t *flags,
>> +					     uint32_t *gpu_id)
>> +{
>> +	struct amdkfd_process_info *info = kgd_info;
>> +	struct dma_buf *dma_buf;
>> +	struct kgd_mem *mem;
>> +	int ret = -EINVAL;
>> +
>> +	if (!info)
>> +		return -EINVAL;
>> +
>> +	dma_buf = dma_buf_get(fd);
>> +	if (IS_ERR(dma_buf))
>> +		return PTR_ERR(dma_buf);
>> +
>> +	mutex_lock(&info->lock);
>> +	list_for_each_entry(mem, &info->kfd_bo_list, validate_list) {
>> +		struct amdgpu_device *bo_adev;
>> +		struct kfd_dev *kfd;
>> +		int8_t xcp_id;
>> +
>> +		if (!mem->is_imported || mem->dmabuf != dma_buf)
>> +			continue;
>> +
>> +		if (size)
>> +			*size = amdgpu_bo_size(mem->bo);
>> +		if (flags)
>> +			*flags = mem->alloc_flags;
>> +		if (gpu_id) {
>> +			bo_adev = amdgpu_ttm_adev(mem->bo->tbo.bdev);
>> +			kfd = bo_adev->kfd.dev;
>> +			xcp_id = mem->bo->xcp_id;
>> +			if (kfd && xcp_id >= 0 && xcp_id < kfd->num_nodes &&
>> +			    kfd->nodes[xcp_id])
>> +				*gpu_id = kfd->nodes[xcp_id]->id;
>> +			else if (kfd && kfd->num_nodes && kfd->nodes[0])
>> +				*gpu_id = kfd->nodes[0]->id;
>> +		}
>> +		ret = 0;
>> +		break;
>> +	}
>> +	mutex_unlock(&info->lock);
>> +	dma_buf_put(dma_buf);
>> +	return ret;
>> +}
>> +
>>   int amdgpu_amdkfd_gpuvm_import_dmabuf_fd(struct amdgpu_device *adev, int fd,
>>   					 uint64_t va, void *drm_priv,
>>   					 struct kgd_mem **mem, uint64_t *size,
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>> index 1d86ddfd6bde..9ca20331e815 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>> @@ -1595,8 +1595,17 @@ static int kfd_ioctl_get_dmabuf_info(struct file *filep,
>>   					  &dmabuf_adev, &args->size,
>>   					  &metadata_buffer, args->metadata_size,
>>   					  &args->metadata_size, &flags, &xcp_id);
>> -	if (r)
>> +	if (r) {
>> +		/* Foreign dma-buf: report it when this process imported it. */
>> +		r = amdgpu_amdkfd_gpuvm_imported_dmabuf_info(p->kgd_process_info,
>> +							     args->dmabuf_fd,
>> +							     &args->size,
>> +							     &args->flags,
>> +							     &args->gpu_id);
>> +		if (!r)
>> +			args->metadata_size = 0;
>>   		goto exit;
>> +	}
>>   
>>   	if (xcp_id >= 0)
>>   		args->gpu_id = dmabuf_adev->kfd.dev->nodes[xcp_id]->id;

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