[PATCH] amd/amdkfd: Trigger segfault for early userptr unmmapping

[Christian König]

On 4/23/25 11:50, Shane Xiao wrote:
> If applications unmap the memory before destroying the userptr, it needs
> trigger a segfault to notify user space to correct the free sequence in
> VM debug mode.
> 
> Signed-off-by: Shane Xiao <shane.xiao at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index d2ec4130a316..259b38424b7f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -2559,6 +2559,16 @@ static int update_invalid_user_pages(struct amdkfd_process_info *process_info,
>  			if (ret != -EFAULT)
>  				return ret;
>  
> +			/* If applications unmaps memory before destroying the userptr
> +			 * from the KFD, trigger a segmentation fault in VM debug mode.
> +			 */
> +			if (amdgpu_ttm_adev(bo->tbo.bdev)->debug_vm) {

Using debug_vm works for now, but maybe we should have a separate debug flag for this.

> +				amdgpu_ttm_tt_get_userptr(&bo->tbo, userptr);
> +				pr_err("User space unmap memory before destroying a userptr that refers to it\n");
> +				pr_err("The unmap userptr address is 0x%llx\n", userptr);
> +				send_sig(SIGSEGV, get_pid_task(process_info->pid, PIDTYPE_PID), 0);

Drivers should *never* mess with send_sig() directly. We made the mistake to allow that with the KFD already.

We should rather send this as GPU access fault or something like that.

Regards,
Christian.

> +			}
> +
>  			ret = 0;
>  		}
>