Message-ID: <20250822-gpuva-mutex-in-gem-v2-3-c41a10d1d3b9@google.com>
Date: Fri, 22 Aug 2025 09:28:26 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Danilo Krummrich <dakr@...nel.org>, Boris Brezillon <boris.brezillon@...labora.com>, 
	Daniel Almeida <daniel.almeida@...labora.com>, Steven Price <steven.price@....com>, 
	Liviu Dudau <liviu.dudau@....com>, Rob Clark <robin.clark@....qualcomm.com>, 
	Rob Herring <robh@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v2 3/3] gpuvm: remove gem.gpuva.lock_dep_map

Since all users of gem.gpuva.lock_dep_map now rely on the mutex directly
in gpuva, we may remove it. Whether the mutex is used is now tracked by
a flag in gpuvm rather than by whether lock_dep_map is null.

Note that a GEM object may not be pushed to multiple gpuvms that
disagree on the value of this new flag. But that's okay because a single
driver should use the same locking scheme everywhere, and a GEM object
is driver specific (when a GEM is exported with prime, a new GEM object
instance is created from the backing dma-buf).

The flag is present even with CONFIG_LOCKDEP=n because the intent is
that the flag will also cause vm_bo cleanup to become deferred. However,
that will happen in a follow-up patch.

Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 drivers/gpu/drm/drm_gpuvm.c           | 30 +++++++++++++--------------
 drivers/gpu/drm/panthor/panthor_gem.c |  1 -
 drivers/gpu/drm/panthor/panthor_mmu.c |  5 +++--
 include/drm/drm_gem.h                 | 39 ++++++++++++++---------------------
 include/drm/drm_gpuvm.h               | 30 ++++++++++++++++++++++++---
 5 files changed, 59 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
index d6bea8a4fffd7613fb9b9ed5c795df373da2e7b6..78a1a4f095095e9379bdf604d583f6c8b9863ccb 100644
--- a/drivers/gpu/drm/drm_gpuvm.c
+++ b/drivers/gpu/drm/drm_gpuvm.c
@@ -497,8 +497,7 @@
  * DRM GPUVM also does not take care of the locking of the backing
  * &drm_gem_object buffers GPU VA lists and &drm_gpuvm_bo abstractions by
  * itself; drivers are responsible to enforce mutual exclusion using either the
- * GEMs dma_resv lock or alternatively a driver specific external lock. For the
- * latter see also drm_gem_gpuva_set_lock().
+ * GEMs dma_resv lock or the GEMs gpuva.lock mutex.
  *
  * However, DRM GPUVM contains lockdep checks to ensure callers of its API hold
  * the corresponding lock whenever the &drm_gem_objects GPU VA list is accessed
@@ -1582,7 +1581,7 @@ drm_gpuvm_bo_destroy(struct kref *kref)
 	drm_gpuvm_bo_list_del(vm_bo, extobj, lock);
 	drm_gpuvm_bo_list_del(vm_bo, evict, lock);
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(gpuvm, obj);
 	list_del(&vm_bo->list.entry.gem);
 
 	if (ops && ops->vm_bo_free)
@@ -1603,7 +1602,8 @@ drm_gpuvm_bo_destroy(struct kref *kref)
  * If the reference count drops to zero, the &gpuvm_bo is destroyed, which
  * includes removing it from the GEMs gpuva list. Hence, if a call to this
  * function can potentially let the reference count drop to zero the caller must
- * hold the dma-resv or driver specific GEM gpuva lock.
+ * hold the lock that the GEM uses for its gpuva list (either the GEM's
+ * dma-resv or gpuva.lock mutex).
  *
  * This function may only be called from non-atomic context.
  *
@@ -1627,7 +1627,7 @@ __drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
 {
 	struct drm_gpuvm_bo *vm_bo;
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(gpuvm, obj);
 	drm_gem_for_each_gpuvm_bo(vm_bo, obj)
 		if (vm_bo->vm == gpuvm)
 			return vm_bo;
@@ -1686,7 +1686,7 @@ drm_gpuvm_bo_obtain(struct drm_gpuvm *gpuvm,
 	if (!vm_bo)
 		return ERR_PTR(-ENOMEM);
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(gpuvm, obj);
 	list_add_tail(&vm_bo->list.entry.gem, &obj->gpuva.list);
 
 	return vm_bo;
@@ -1722,7 +1722,7 @@ drm_gpuvm_bo_obtain_prealloc(struct drm_gpuvm_bo *__vm_bo)
 		return vm_bo;
 	}
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(gpuvm, obj);
 	list_add_tail(&__vm_bo->list.entry.gem, &obj->gpuva.list);
 
 	return __vm_bo;
@@ -1894,8 +1894,7 @@ EXPORT_SYMBOL_GPL(drm_gpuva_remove);
  * reference of the latter is taken.
  *
  * This function expects the caller to protect the GEM's GPUVA list against
- * concurrent access using either the GEMs dma_resv lock or a driver specific
- * lock set through drm_gem_gpuva_set_lock().
+ * concurrent access using either the GEM's dma-resv or gpuva.lock mutex.
  */
 void
 drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuvm_bo *vm_bo)
@@ -1910,7 +1909,7 @@ drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuvm_bo *vm_bo)
 
 	va->vm_bo = drm_gpuvm_bo_get(vm_bo);
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(gpuvm, obj);
 	list_add_tail(&va->gem.entry, &vm_bo->list.gpuva);
 }
 EXPORT_SYMBOL_GPL(drm_gpuva_link);
@@ -1930,8 +1929,7 @@ EXPORT_SYMBOL_GPL(drm_gpuva_link);
  * the latter is dropped.
  *
  * This function expects the caller to protect the GEM's GPUVA list against
- * concurrent access using either the GEMs dma_resv lock or a driver specific
- * lock set through drm_gem_gpuva_set_lock().
+ * concurrent access using either the GEM's dma-resv or gpuva.lock mutex.
  */
 void
 drm_gpuva_unlink(struct drm_gpuva *va)
@@ -1942,7 +1940,7 @@ drm_gpuva_unlink(struct drm_gpuva *va)
 	if (unlikely(!obj))
 		return;
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	drm_gem_gpuva_assert_lock_held(va->vm, obj);
 	list_del_init(&va->gem.entry);
 
 	va->vm_bo = NULL;
@@ -2943,8 +2941,8 @@ EXPORT_SYMBOL_GPL(drm_gpuvm_prefetch_ops_create);
  * After the caller finished processing the returned &drm_gpuva_ops, they must
  * be freed with &drm_gpuva_ops_free.
  *
- * It is the callers responsibility to protect the GEMs GPUVA list against
- * concurrent access using the GEMs dma_resv lock.
+ * This function expects the caller to protect the GEM's GPUVA list against
+ * concurrent access using either the GEM's dma-resv or gpuva.lock mutex.
  *
  * Returns: a pointer to the &drm_gpuva_ops on success, an ERR_PTR on failure
  */
@@ -2956,7 +2954,7 @@ drm_gpuvm_bo_unmap_ops_create(struct drm_gpuvm_bo *vm_bo)
 	struct drm_gpuva *va;
 	int ret;
 
-	drm_gem_gpuva_assert_lock_held(vm_bo->obj);
+	drm_gem_gpuva_assert_lock_held(vm_bo->vm, vm_bo->obj);
 
 	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
 	if (!ops)
diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index c654a3377903cf7e067becdb481fb14895a4eaa5..156c7a0b62a231219645095d6012a5b108130bbc 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -245,7 +245,6 @@ struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t
 
 	obj->base.base.funcs = &panthor_gem_funcs;
 	obj->base.map_wc = !ptdev->coherent;
-	drm_gem_gpuva_set_lock(&obj->base.base, &obj->base.base.gpuva.lock);
 	mutex_init(&obj->label.lock);
 
 	panthor_gem_debugfs_bo_init(obj);
diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 2881942ab5115686803fb9d9036bc059d56b7fa3..ee9e94448b76ffd31a97d82a857fa925c4cf0cb5 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -2420,8 +2420,9 @@ panthor_vm_create(struct panthor_device *ptdev, bool for_mcu,
 	 * to be handled the same way user VMAs are.
 	 */
 	drm_gpuvm_init(&vm->base, for_mcu ? "panthor-MCU-VM" : "panthor-GPU-VM",
-		       DRM_GPUVM_RESV_PROTECTED, &ptdev->base, dummy_gem,
-		       min_va, va_range, 0, 0, &panthor_gpuvm_ops);
+		       DRM_GPUVM_RESV_PROTECTED | DRM_GPUVM_IMMEDIATE_MODE,
+		       &ptdev->base, dummy_gem, min_va, va_range, 0, 0,
+		       &panthor_gpuvm_ops);
 	drm_gem_object_put(dummy_gem);
 	return vm;
 
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 5934d8dc267a65aaf62d2d025869221cd110b325..85a25bbb387c4590678e4ba243b51acd94b008ed 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -402,17 +402,22 @@ struct drm_gem_object {
 	 *
 	 * Provides the list of GPU VAs attached to this GEM object.
 	 *
-	 * Drivers should lock list accesses with the GEMs &dma_resv lock
-	 * (&drm_gem_object.resv) or a custom lock if one is provided. The
-	 * mutex inside this struct may be used as the custom lock.
+	 * When DRM_GPUVM_IMMEDIATE_MODE is set, this list is protected by the
+	 * mutex. Otherwise, the list is protected by the GEMs &dma_resv lock.
+	 *
+	 * Note that all entries in this list must agree on whether
+	 * DRM_GPUVM_IMMEDIATE_MODE is set.
 	 */
 	struct {
 		struct list_head list;
 
+		/**
+		 * @gpuva.lock: Only used when DRM_GPUVM_IMMEDIATE_MODE is set.
+		 * It should be safe to take this mutex during the fence
+		 * signalling path, so do not allocate memory while holding
+		 * this lock.
+		 */
 		struct mutex lock;
-#ifdef CONFIG_LOCKDEP
-		struct lockdep_map *lock_dep_map;
-#endif
 	} gpuva;
 
 	/**
@@ -597,26 +602,12 @@ static inline bool drm_gem_is_imported(const struct drm_gem_object *obj)
 }
 
 #ifdef CONFIG_LOCKDEP
-/**
- * drm_gem_gpuva_set_lock() - Set the lock protecting accesses to the gpuva list.
- * @obj: the &drm_gem_object
- * @lock: the lock used to protect the gpuva list. The locking primitive
- * must contain a dep_map field.
- *
- * Call this if you're not proctecting access to the gpuva list with the
- * dma-resv lock, but with a custom lock.
- */
-#define drm_gem_gpuva_set_lock(obj, lock) \
-	if (!WARN((obj)->gpuva.lock_dep_map, \
-		  "GEM GPUVA lock should be set only once.")) \
-		(obj)->gpuva.lock_dep_map = &(lock)->dep_map
-#define drm_gem_gpuva_assert_lock_held(obj) \
-	lockdep_assert((obj)->gpuva.lock_dep_map ? \
-		       lock_is_held((obj)->gpuva.lock_dep_map) : \
+#define drm_gem_gpuva_assert_lock_held(gpuvm, obj) \
+	lockdep_assert(drm_gpuvm_immediate_mode(gpuvm) ? \
+		       lock_is_held(&(obj)->gpuva.lock.dep_map) : \
 		       dma_resv_held((obj)->resv))
 #else
-#define drm_gem_gpuva_set_lock(obj, lock) do {} while (0)
-#define drm_gem_gpuva_assert_lock_held(obj) do {} while (0)
+#define drm_gem_gpuva_assert_lock_held(gpuvm, obj) do {} while (0)
 #endif
 
 /**
diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
index 4a22b9d848f7b3d5710ca554f5b01556abf95985..598ba376b9430cdd4ab7bacdc15de031a887cf71 100644
--- a/include/drm/drm_gpuvm.h
+++ b/include/drm/drm_gpuvm.h
@@ -196,10 +196,20 @@ enum drm_gpuvm_flags {
 	 */
 	DRM_GPUVM_RESV_PROTECTED = BIT(0),
 
+	/**
+	 * @DRM_GPUVM_IMMEDIATE_MODE: use the locking scheme that makes it safe
+	 * to modify the GPUVM during the fence signalling path
+	 *
+	 * When set, gpuva.lock is used to protect gpuva.list in all GEM
+	 * objects associated with this GPUVM. Otherwise, the GEMs dma-resv is
+	 * used.
+	 */
+	DRM_GPUVM_IMMEDIATE_MODE = BIT(1),
+
 	/**
 	 * @DRM_GPUVM_USERBITS: user defined bits
 	 */
-	DRM_GPUVM_USERBITS = BIT(1),
+	DRM_GPUVM_USERBITS = BIT(2),
 };
 
 /**
@@ -369,6 +379,19 @@ drm_gpuvm_resv_protected(struct drm_gpuvm *gpuvm)
 	return gpuvm->flags & DRM_GPUVM_RESV_PROTECTED;
 }
 
+/**
+ * drm_gpuvm_immediate_mode() - indicates whether &DRM_GPUVM_IMMEDIATE_MODE is
+ * set
+ * @gpuvm: the &drm_gpuvm
+ *
+ * Returns: true if &DRM_GPUVM_IMMEDIATE_MODE is set, false otherwise.
+ */
+static inline bool
+drm_gpuvm_immediate_mode(struct drm_gpuvm *gpuvm)
+{
+	return gpuvm->flags & DRM_GPUVM_IMMEDIATE_MODE;
+}
+
 /**
  * drm_gpuvm_resv() - returns the &drm_gpuvm's &dma_resv
  * @gpuvm__: the &drm_gpuvm
@@ -742,9 +765,10 @@ drm_gpuvm_bo_gem_evict(struct drm_gem_object *obj, bool evict)
 {
 	struct drm_gpuvm_bo *vm_bo;
 
-	drm_gem_gpuva_assert_lock_held(obj);
-	drm_gem_for_each_gpuvm_bo(vm_bo, obj)
+	drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
+		drm_gem_gpuva_assert_lock_held(vm_bo->vm, obj);
 		drm_gpuvm_bo_evict(vm_bo, evict);
+	}
 }
 
 void drm_gpuvm_bo_extobj_add(struct drm_gpuvm_bo *vm_bo);

-- 
2.51.0.rc2.233.g662b1ed5c5-goog

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