[PATCH] drm/amdkfd: Remove skiping userptr buffer mapping when mmu notifier marks it as invalid

[Felix Kuehling]

Am 2023-05-09 um 18:17 schrieb Alex Deucher:
> From: Xiaogang Chen <xiaogang.chen at amd.com>
>
> mmu notifier does not always hold mm->sem during call back. That causes
> a race condition between kfd userprt buffer mapping and mmu notifier
> which leds to gpu shadder or SDMA access userptr buffer before it has been
> mapped to gpu VM. Always map userptr buffer to avoid that though it may make
> some userprt buffers mapped two times.
>
> Suggested-by: Felix Kuehling <Felix.Kuehling at amd.com>
> Signed-off-by: Xiaogang Chen <xiaogang.chen at amd.com>
> Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>

This patch is no longer needed and should not be applied. It was 
originally applied to amd-staging-drm-next as patch 
fcf00f8d29f2fc6bf00531a1447be28b99073cc3 in November 2022. This fixed a 
race condition due to incorrect assumptions about the mmap lock and MMU 
notifiers. This hunk was added back by my later patch f95f51a4c335 
("drm/amdgpu: Add notifier lock for KFD userptrs") in December, using 
our own notifier lock that doesn't suffer from those races.

Regards,
   Felix


> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 10 ----------
>   1 file changed, 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index 58a774647573..40078c0a5585 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -1942,16 +1942,6 @@ int amdgpu_amdkfd_gpuvm_map_memory_to_gpu(
>   	 */
>   	mutex_lock(&mem->process_info->lock);
>   
> -	/* Lock notifier lock. If we find an invalid userptr BO, we can be
> -	 * sure that the MMU notifier is no longer running
> -	 * concurrently and the queues are actually stopped
> -	 */
> -	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm)) {
> -		mutex_lock(&mem->process_info->notifier_lock);
> -		is_invalid_userptr = !!mem->invalid;
> -		mutex_unlock(&mem->process_info->notifier_lock);
> -	}
> -
>   	mutex_lock(&mem->lock);
>   
>   	domain = mem->domain;