Re: [PATCH v3 1/2] drm/amdgpu: convert amdgpu_vm_lock_by_pasid() to drm_exec

[Christian König]

On 5/20/26 17:17, Mikhail Gavrilov wrote:
> amdgpu_vm_lock_by_pasid() looks up a VM by PASID and reserves its root
> PD with a bare amdgpu_bo_reserve(), returning the still-reserved root to
> the caller. A caller that then needs to reserve further BOs (for example
> the devcoredump IB dump) ends up nesting reservation_ww_class_mutex
> acquires without a ww_acquire_ctx, which lockdep flags as recursive
> locking.
> 
> Convert the helper to take a drm_exec context and lock the root PD via
> amdgpu_vm_lock_pd() instead. Callers now run it inside a
> drm_exec_until_all_locked() loop and can lock additional BOs in the same
> ww ticket, so there is no nested ww_mutex acquire.
> 
> The only existing caller, amdgpu_vm_handle_fault(), is updated
> accordingly. Its is_compute_context path, which previously dropped the
> root reservation around svm_range_restore_pages() and re-took it, now
> finalises the drm_exec context and re-initialises a fresh one; behaviour
> is otherwise unchanged.
> 
> No functional change intended for the page-fault path.
> 
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 72 ++++++++++++++++++--------
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h |  3 +-
>  2 files changed, 51 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index 9ba9de16a27a..3a22670b733f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -2950,14 +2950,22 @@ int amdgpu_vm_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
>  }
>  
>  /**
> - * amdgpu_vm_lock_by_pasid - return an amdgpu_vm and its root bo from a pasid, if possible.
> + * amdgpu_vm_lock_by_pasid - look up a VM by PASID and lock its root PD
>   * @adev: amdgpu device pointer
> - * @root: root BO of the VM
> + * @root: out: reference to the VM's root BO, dropped by the caller
>   * @pasid: PASID of the VM
> - * The caller needs to unreserve and unref the root bo on success.
> + * @exec: drm_exec context to lock the root PD in
> + *
> + * Must be called from within a drm_exec_until_all_locked() loop; the caller
> + * runs drm_exec_retry_on_contention() afterwards and drops the *root
> + * reference once the drm_exec context is finalised.
> + *
> + * Return: the VM on success, or NULL if the PASID has no VM, the VM is being
> + * torn down, or locking the root PD failed.
>   */
>  struct amdgpu_vm *amdgpu_vm_lock_by_pasid(struct amdgpu_device *adev,
> -					  struct amdgpu_bo **root, u32 pasid)
> +					  struct amdgpu_bo **root, u32 pasid,

I think we can drop the root parameter now, the exec reference should be sufficient.

> +					  struct drm_exec *exec)
>  {
>  	unsigned long irqflags;
>  	struct amdgpu_vm *vm;
> @@ -2971,9 +2979,11 @@ struct amdgpu_vm *amdgpu_vm_lock_by_pasid(struct amdgpu_device *adev,
>  	if (!*root)
>  		return NULL;
>  
> -	r = amdgpu_bo_reserve(*root, true);
> -	if (r)
> -		goto error_unref;
> +	r = amdgpu_vm_lock_pd(vm, exec, 0);

amdgpu_vm_lock_pd() can't be used here since we can't gurantee that the VM pointer wouldn't go away.

Just do:

r = drm_exec_lock_obj(exec, root->tbo.base);

> +	if (r) {
> +		amdgpu_bo_unref(root);
> +		return NULL;
> +	}
>  
>  	/* Double check that the VM still exists */
>  	xa_lock_irqsave(&adev->vm_manager.pasids, irqflags);
> @@ -2981,16 +2991,12 @@ struct amdgpu_vm *amdgpu_vm_lock_by_pasid(struct amdgpu_device *adev,
>  	if (vm && vm->root.bo != *root)
>  		vm = NULL;
>  	xa_unlock_irqrestore(&adev->vm_manager.pasids, irqflags);
> -	if (!vm)
> -		goto error_unlock;
> +	if (!vm) {

We should cleanup with drm_exec_unlock_obj() here, same as it was before.

> +		amdgpu_bo_unref(root);
> +		return NULL;
> +	}
>  
>  	return vm;

We can drop the extra reference on the root BO before returning the VM now since the drm_exec object holds one as well.

Apart from that this looks like a really nice cleanup to me.

Thanks,
Christian.

> -error_unlock:
> -	amdgpu_bo_unreserve(*root);
> -
> -error_unref:
> -	amdgpu_bo_unref(root);
> -	return NULL;
>  }
>  
>  /**
> @@ -3013,20 +3019,32 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
>  {
>  	bool is_compute_context = false;
>  	struct amdgpu_bo *root;
> +	struct drm_exec exec;
>  	uint64_t value, flags;
>  	struct amdgpu_vm *vm;
>  	int r;
>  
> -	vm = amdgpu_vm_lock_by_pasid(adev, &root, pasid);
> -	if (!vm)
> +	drm_exec_init(&exec, 0, 0);
> +	drm_exec_until_all_locked(&exec) {
> +		vm = amdgpu_vm_lock_by_pasid(adev, &root, pasid, &exec);
> +		drm_exec_retry_on_contention(&exec);
> +		if (!vm)
> +			break;
> +	}
> +	if (!vm) {
> +		drm_exec_fini(&exec);
>  		return false;
> +	}
>  
>  	is_compute_context = vm->is_compute_context;
>  
>  	if (is_compute_context) {
> -		/* Unreserve root since svm_range_restore_pages might try to reserve it. */
> -		/* TODO: rework svm_range_restore_pages so that this isn't necessary. */
> -		amdgpu_bo_unreserve(root);
> +		/* Release the root PD lock since svm_range_restore_pages
> +		 * might try to take it.
> +		 * TODO: rework svm_range_restore_pages so that this isn't
> +		 * necessary.
> +		 */
> +		drm_exec_fini(&exec);
>  
>  		if (!svm_range_restore_pages(adev, pasid, vmid,
>  					     node_id, addr >> PAGE_SHIFT, ts, write_fault)) {
> @@ -3036,9 +3054,17 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
>  		amdgpu_bo_unref(&root);
>  
>  		/* Re-acquire the VM lock, could be that the VM was freed in between. */
> -		vm = amdgpu_vm_lock_by_pasid(adev, &root, pasid);
> -		if (!vm)
> +		drm_exec_init(&exec, 0, 0);
> +		drm_exec_until_all_locked(&exec) {
> +			vm = amdgpu_vm_lock_by_pasid(adev, &root, pasid, &exec);
> +			drm_exec_retry_on_contention(&exec);
> +			if (!vm)
> +				break;
> +		}
> +		if (!vm) {
> +			drm_exec_fini(&exec);
>  			return false;
> +		}
>  	}
>  
>  	addr /= AMDGPU_GPU_PAGE_SIZE;
> @@ -3076,7 +3102,7 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
>  	r = amdgpu_vm_update_pdes(adev, vm, true);
>  
>  error_unlock:
> -	amdgpu_bo_unreserve(root);
> +	drm_exec_fini(&exec);
>  	if (r < 0)
>  		dev_err(adev->dev, "Can't handle page fault (%d)\n", r);
>  
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> index d083d7aab75c..af292c2fc521 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> @@ -593,7 +593,8 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
>  			    bool write_fault);
>  
>  struct amdgpu_vm *amdgpu_vm_lock_by_pasid(struct amdgpu_device *adev,
> -					  struct amdgpu_bo **root, u32 pasid);
> +					  struct amdgpu_bo **root, u32 pasid,
> +					  struct drm_exec *exec);
>  
>  void amdgpu_vm_set_task_info(struct amdgpu_vm *vm);
>