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

[Felix Kuehling <felix.kuehling@amd.com>]

On 2024-05-09 16:06, 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
> v3: Use crc16 as suggested-by: Lijo Lazar <lijo.lazar@amd.com>
>      Ensure that gpu_id != 0
>
> Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>

Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>


> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_topology.c | 40 +++++++++++++++++++----
>   1 file changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> index 219dcf504f24..4954a3021f70 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
> @@ -31,6 +31,7 @@
>   #include <linux/log2.h>
>   #include <linux/dmi.h>
>   #include <linux/atomic.h>
> +#include <linux/crc16.h>
>   
>   #include "kfd_priv.h"
>   #include "kfd_crat.h"
> @@ -1091,14 +1092,17 @@ void kfd_topology_shutdown(void)
>   
>   static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>   {
> -	uint32_t hashout;
> +	uint32_t gpu_id;
>   	uint32_t buf[8];
>   	uint64_t local_mem_size;
> -	int i;
> +	struct kfd_topology_device *dev;
> +	bool is_unique;
> +	uint8_t *crc_buf;
>   
>   	if (!gpu)
>   		return 0;
>   
> +	crc_buf = (uint8_t*)&buf;
>   	local_mem_size = gpu->local_mem_info.local_mem_size_private +
>   			gpu->local_mem_info.local_mem_size_public;
>   	buf[0] = gpu->adev->pdev->devfn;
> @@ -1111,10 +1115,34 @@ static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>   	buf[6] = upper_32_bits(local_mem_size);
>   	buf[7] = (ffs(gpu->xcc_mask) - 1) | (NUM_XCC(gpu->xcc_mask) << 16);
>   
> -	for (i = 0, hashout = 0; i < 8; i++)
> -		hashout ^= hash_32(buf[i], KFD_GPU_ID_HASH_WIDTH);
> +	gpu_id = crc16(0, crc_buf, sizeof(buf)) &
> +		 ((1 << KFD_GPU_ID_HASH_WIDTH) - 1);
>   
> -	return hashout;
> +	/* There is a very small possibility when generating a
> +	 * 16 (KFD_GPU_ID_HASH_WIDTH) bit value from 8 word buffer
> +	 * that the value could be 0 or non-unique. So, check if
> +	 * it is unique and non-zero. If not unique increment till
> +	 * unique one is found. In case of overflow, restart from 1
> +	 */
> +
> +	down_read(&topology_lock);
> +	do {
> +		is_unique = true;
> +		if (!gpu_id)
> +			gpu_id = 1;
> +		list_for_each_entry(dev, &topology_device_list, list) {
> +			if (dev->gpu && dev->gpu_id == gpu_id) {
> +				is_unique = false;
> +				break;
> +			}
> +		}
> +		if (unlikely(!is_unique))
> +			gpu_id = (gpu_id + 1) &
> +				  ((1 << KFD_GPU_ID_HASH_WIDTH) - 1);
> +	} while (!is_unique);
> +	up_read(&topology_lock);
> +
> +	return gpu_id;
>   }
>   /* kfd_assign_gpu - Attach @gpu to the correct kfd topology device. If
>    *		the GPU device is not already present in the topology device
> @@ -1945,7 +1973,6 @@ 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.");
> @@ -1968,6 +1995,7 @@ 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;
>