drm/i915: Don't free shared locks while shared

We are currently sharing the VM reservation locks across a number of
gem objects with page-table memory. Since TTM will individiualize the
reservation locks when freeing objects, including accessing the shared
locks, make sure that the shared locks are not freed until that is done.
For PPGTT we add an additional refcount, for GGTT we take additional
measures to make sure objects sharing the GGTT reservation lock are
freed at GGTT takedown

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210601074654.3103-3-thomas.hellstrom@linux.intel.com

1 files changed, 37 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
index 9b98f9d9faa3..94849567143d 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
@@ -22,8 +22,11 @@ struct drm_i915_gem_object *alloc_pt_lmem(struct i915_address_space *vm, int sz)
 	 * object underneath, with the idea that one object_lock() will lock
 	 * them all at once.
 	 */
-	if (!IS_ERR(obj))
-		obj->base.resv = &vm->resv;
+	if (!IS_ERR(obj)) {
+		obj->base.resv = i915_vm_resv_get(vm);
+		obj->shares_resv_from = vm;
+	}
+
 	return obj;
 }
 
@@ -40,8 +43,11 @@ struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz)
 	 * object underneath, with the idea that one object_lock() will lock
 	 * them all at once.
 	 */
-	if (!IS_ERR(obj))
-		obj->base.resv = &vm->resv;
+	if (!IS_ERR(obj)) {
+		obj->base.resv = i915_vm_resv_get(vm);
+		obj->shares_resv_from = vm;
+	}
+
 	return obj;
 }
 
@@ -102,7 +108,7 @@ void __i915_vm_close(struct i915_address_space *vm)
 int i915_vm_lock_objects(struct i915_address_space *vm,
 			 struct i915_gem_ww_ctx *ww)
 {
-	if (vm->scratch[0]->base.resv == &vm->resv) {
+	if (vm->scratch[0]->base.resv == &vm->_resv) {
 		return i915_gem_object_lock(vm->scratch[0], ww);
 	} else {
 		struct i915_ppgtt *ppgtt = i915_vm_to_ppgtt(vm);
@@ -118,6 +124,22 @@ void i915_address_space_fini(struct i915_address_space *vm)
 	mutex_destroy(&vm->mutex);
 }
 
+/**
+ * i915_vm_resv_release - Final struct i915_address_space destructor
+ * @kref: Pointer to the &i915_address_space.resv_ref member.
+ *
+ * This function is called when the last lock sharer no longer shares the
+ * &i915_address_space._resv lock.
+ */
+void i915_vm_resv_release(struct kref *kref)
+{
+	struct i915_address_space *vm =
+		container_of(kref, typeof(*vm), resv_ref);
+
+	dma_resv_fini(&vm->_resv);
+	kfree(vm);
+}
+
 static void __i915_vm_release(struct work_struct *work)
 {
 	struct i915_address_space *vm =
@@ -125,9 +147,8 @@ static void __i915_vm_release(struct work_struct *work)
 
 	vm->cleanup(vm);
 	i915_address_space_fini(vm);
-	dma_resv_fini(&vm->resv);
 
-	kfree(vm);
+	i915_vm_resv_put(vm);
 }
 
 void i915_vm_release(struct kref *kref)
@@ -144,6 +165,14 @@ void i915_vm_release(struct kref *kref)
 void i915_address_space_init(struct i915_address_space *vm, int subclass)
 {
 	kref_init(&vm->ref);
+
+	/*
+	 * Special case for GGTT that has already done an early
+	 * kref_init here.
+	 */
+	if (!kref_read(&vm->resv_ref))
+		kref_init(&vm->resv_ref);
+
 	INIT_RCU_WORK(&vm->rcu, __i915_vm_release);
 	atomic_set(&vm->open, 1);
 
@@ -170,7 +199,7 @@ void i915_address_space_init(struct i915_address_space *vm, int subclass)
 		might_alloc(GFP_KERNEL);
 		mutex_release(&vm->mutex.dep_map, _THIS_IP_);
 	}
-	dma_resv_init(&vm->resv);
+	dma_resv_init(&vm->_resv);
 
 	GEM_BUG_ON(!vm->total);
 	drm_mm_init(&vm->mm, 0, vm->total);