[PATCH v5 1/2] drm/amdgpu: convert amdgpu_vm_lock_by_pasid() to drm_exec

[Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>]

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 with
drm_exec_lock_obj(). 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 drm_exec context holds its own reference on the locked root BO, so
the helper no longer hands a root reference back to the caller: the
root output parameter is dropped, and the transient reference taken
across the PASID lookup is released before returning.

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.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 91 ++++++++++++++++----------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h |  2 +-
 2 files changed, 58 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 9ba9de16a27a..d734d8c0de6e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -2950,47 +2950,56 @@ 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
  * @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. The drm_exec context holds
+ * a reference on the root BO until it 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)
+					  u32 pasid, struct drm_exec *exec)
 {
 	unsigned long irqflags;
+	struct amdgpu_bo *root;
 	struct amdgpu_vm *vm;
 	int r;
 
 	xa_lock_irqsave(&adev->vm_manager.pasids, irqflags);
 	vm = xa_load(&adev->vm_manager.pasids, pasid);
-	*root = vm ? amdgpu_bo_ref(vm->root.bo) : NULL;
+	root = vm ? amdgpu_bo_ref(vm->root.bo) : NULL;
 	xa_unlock_irqrestore(&adev->vm_manager.pasids, irqflags);
 
-	if (!*root)
+	if (!root)
 		return NULL;
 
-	r = amdgpu_bo_reserve(*root, true);
-	if (r)
-		goto error_unref;
+	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);
 	vm = xa_load(&adev->vm_manager.pasids, pasid);
-	if (vm && vm->root.bo != *root)
+	if (vm && vm->root.bo != root)
 		vm = NULL;
 	xa_unlock_irqrestore(&adev->vm_manager.pasids, irqflags);
-	if (!vm)
-		goto error_unlock;
+	if (!vm) {
+		drm_exec_unlock_obj(exec, &root->tbo.base);
+		amdgpu_bo_unref(&root);
+		return NULL;
+	}
 
-	return vm;
-error_unlock:
-	amdgpu_bo_unreserve(*root);
+	/* The drm_exec context holds its own reference on the root BO. */
+	amdgpu_bo_unref(&root);
 
-error_unref:
-	amdgpu_bo_unref(root);
-	return NULL;
+	return vm;
 }
 
 /**
@@ -3012,33 +3021,49 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
 			    uint64_t ts, bool write_fault)
 {
 	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, 1);
+	drm_exec_until_all_locked(&exec) {
+		vm = amdgpu_vm_lock_by_pasid(adev, 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)) {
-			amdgpu_bo_unref(&root);
+					     node_id, addr >> PAGE_SHIFT, ts, write_fault))
 			return true;
-		}
-		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, 1);
+		drm_exec_until_all_locked(&exec) {
+			vm = amdgpu_vm_lock_by_pasid(adev, pasid, &exec);
+			drm_exec_retry_on_contention(&exec);
+			if (!vm)
+				break;
+		}
+		if (!vm) {
+			drm_exec_fini(&exec);
 			return false;
+		}
 	}
 
 	addr /= AMDGPU_GPU_PAGE_SIZE;
@@ -3062,7 +3087,7 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
 		value = 0;
 	}
 
-	r = dma_resv_reserve_fences(root->tbo.base.resv, 1);
+	r = dma_resv_reserve_fences(vm->root.bo->tbo.base.resv, 1);
 	if (r) {
 		pr_debug("failed %d to reserve fence slot\n", r);
 		goto error_unlock;
@@ -3076,12 +3101,10 @@ 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);
 
-	amdgpu_bo_unref(&root);
-
 	return false;
 }
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index d083d7aab75c..0c6e3e0368c7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -593,7 +593,7 @@ 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);
+					  u32 pasid, struct drm_exec *exec);
 
 void amdgpu_vm_set_task_info(struct amdgpu_vm *vm);
 
-- 
2.54.0