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.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250827-gpuva-mutex-in-gem-v3-3-bd89f5a82c0d@google.com
[ Use lockdep_is_held() instead of lock_is_held(). - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

2 files changed, 42 insertions, 29 deletions

diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index a995c0c1b63c..8d48d2af2649 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -399,6 +399,12 @@ struct drm_gem_object {
 
 	/**
 	 * @gpuva: Fields used by GPUVM to manage mappings pointing to this GEM object.
+	 *
+	 * 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 {
 		/**
@@ -412,17 +418,14 @@ struct drm_gem_object {
 
 		/**
 		 * @gpuva.lock: lock protecting access to &drm_gem_object.gpuva.list
-		 * when the resv lock can't be used.
+		 * when DRM_GPUVM_IMMEDIATE_MODE is used.
 		 *
-		 * Should only be used when the VM is being modified in a fence
-		 * signalling path, otherwise you should use &drm_gem_object.resv to
-		 * protect accesses to &drm_gem_object.gpuva.list.
+		 * 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. Otherwise,
+		 * the &dma_resv lock should be used.
 		 */
 		struct mutex lock;
-
-#ifdef CONFIG_LOCKDEP
-		struct lockdep_map *lock_dep_map;
-#endif
 	} gpuva;
 
 	/**
@@ -607,26 +610,12 @@ 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) ? \
+		       lockdep_is_held(&(obj)->gpuva.lock) : \
 		       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 4a22b9d848f7..727b8f336fad 100644
--- a/include/drm/drm_gpuvm.h
+++ b/include/drm/drm_gpuvm.h
@@ -197,9 +197,19 @@ enum drm_gpuvm_flags {
 	DRM_GPUVM_RESV_PROTECTED = BIT(0),
 
 	/**
+	 * @DRM_GPUVM_IMMEDIATE_MODE: use the locking scheme for GEMs designed
+	 * for modifying 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),
 };
 
 /**
@@ -370,6 +380,19 @@ drm_gpuvm_resv_protected(struct drm_gpuvm *gpuvm)
 }
 
 /**
+ * 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);