Re: [PATCH] drm/amdkfd: Ensure gpu_id is unique

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 5/4/2024 3:36 AM, Harish Kasiviswanathan wrote:
> gpu_id needs to be unique for user space to identify GPUs via KFD
> interface. In the current implementation there is a very small
> probability of having non unique gpu_ids.
> 
> v2: Add check to confirm if gpu_id is unique. If not unique, find one
>     Changed commit header to reflect the above
> 
> Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
> ---
>  drivers/gpu/drm/amd/amdkfd/kfd_topology.c | 26 ++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> index b93913934b03..01d4c2e10c6d 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> @@ -1095,6 +1095,8 @@ static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>  	uint32_t hashout;
>  	uint32_t buf[8];
>  	uint64_t local_mem_size;
> +	struct kfd_topology_device *dev;
> +	bool is_unique;
>  	int i;
>  
>  	if (!gpu)
> @@ -1115,6 +1117,28 @@ static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>  	for (i = 0, hashout = 0; i < 8; i++)
>  		hashout ^= hash_32(buf[i], KFD_GPU_ID_HASH_WIDTH);

Instead of this, suggest to replace this with crc16(). That has a better
chance to avoid collision as it takes into account the whole contents of
the buffer. It may work better than combining hashes with XOR.

Thanks,
Lijo

>  
> +	/* hash generated could be non-unique. Check if it is unique.
> +	 * If not unique increment till unique one is found. In case
> +	 * of overflow, restart from 1
> +	*/
> +	down_read(&topology_lock);
> +	do {
> +		is_unique = true;
> +		list_for_each_entry(dev, &topology_device_list, list) {
> +			if (dev->gpu && dev->gpu_id == hashout) {
> +				is_unique = false;
> +				break;
> +			}
> +		}
> +		if (unlikely(!is_unique)) {
> +			hashout = (hashout + 1) &
> +				  ((1 << KFD_GPU_ID_HASH_WIDTH) - 1);
> +			if (!hashout)
> +				hashout = 1;
> +		}
> +	} while (!is_unique);
> +	up_read(&topology_lock);
> +
>  	return hashout;
>  }
>  /* kfd_assign_gpu - Attach @gpu to the correct kfd topology device. If
> @@ -1946,7 +1970,6 @@ int kfd_topology_add_device(struct kfd_node *gpu)
>  	struct amdgpu_gfx_config *gfx_info = &gpu->adev->gfx.config;
>  	struct amdgpu_cu_info *cu_info = &gpu->adev->gfx.cu_info;
>  
> -	gpu_id = kfd_generate_gpu_id(gpu);
>  	if (gpu->xcp && !gpu->xcp->ddev) {
>  		dev_warn(gpu->adev->dev,
>  			 "Won't add GPU to topology since it has no drm node assigned.");
> @@ -1969,6 +1992,7 @@ int kfd_topology_add_device(struct kfd_node *gpu)
>  	if (res)
>  		return res;
>  
> +	gpu_id = kfd_generate_gpu_id(gpu);
>  	dev->gpu_id = gpu_id;
>  	gpu->id = gpu_id;
>