[PATCH v3 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 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@gmail.com>
---
 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,
+					  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);
+	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) {
+		amdgpu_bo_unref(root);
+		return NULL;
+	}
 
 	return vm;
-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);
 
-- 
2.54.0