drm/gpuvm: Add locking helpers

For UNMAP/REMAP steps we could be needing to lock objects that are not
explicitly listed in the VM_BIND ioctl in order to tear-down unmapped
VAs.  These helpers handle locking/preparing the needed objects.

Note that these functions do not strictly require the VM changes to be
applied before the next drm_gpuvm_sm_map_lock()/_unmap_lock() call.  In
the case that VM changes from an earlier drm_gpuvm_sm_map()/_unmap()
call result in a differing sequence of steps when the VM changes are
actually applied, it will be the same set of GEM objects involved, so
the locking is still correct.

v2: Rename to drm_gpuvm_sm_*_exec_locked() [Danilo]
v3: Expand comments to show expected usage, and explain how the usage
    is safe in the case of overlapping driver VM_BIND ops.

Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Tested-by: Antonino Maniscalco <antomani103@gmail.com>
Reviewed-by: Antonino Maniscalco <antomani103@gmail.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/661458/

drivers/gpu/drm/drm_gpuvm.c

@@ -2391,6 +2391,132 @@ drm_gpuvm_sm_unmap(struct drm_gpuvm *gpuvm, void *priv,
 }
 EXPORT_SYMBOL_GPL(drm_gpuvm_sm_unmap);
 
+static int
+drm_gpuva_sm_step_lock(struct drm_gpuva_op *op, void *priv)
+{
+	struct drm_exec *exec = priv;
+
+	switch (op->op) {
+	case DRM_GPUVA_OP_REMAP:
+		if (op->remap.unmap->va->gem.obj)
+			return drm_exec_lock_obj(exec, op->remap.unmap->va->gem.obj);
+		return 0;
+	case DRM_GPUVA_OP_UNMAP:
+		if (op->unmap.va->gem.obj)
+			return drm_exec_lock_obj(exec, op->unmap.va->gem.obj);
+		return 0;
+	default:
+		return 0;
+	}
+}
+
+static const struct drm_gpuvm_ops lock_ops = {
+	.sm_step_map = drm_gpuva_sm_step_lock,
+	.sm_step_remap = drm_gpuva_sm_step_lock,
+	.sm_step_unmap = drm_gpuva_sm_step_lock,
+};
+
+/**
+ * drm_gpuvm_sm_map_exec_lock() - locks the objects touched by a drm_gpuvm_sm_map()
+ * @gpuvm: the &drm_gpuvm representing the GPU VA space
+ * @exec: the &drm_exec locking context
+ * @num_fences: for newly mapped objects, the # of fences to reserve
+ * @req_addr: the start address of the range to unmap
+ * @req_range: the range of the mappings to unmap
+ * @req_obj: the &drm_gem_object to map
+ * @req_offset: the offset within the &drm_gem_object
+ *
+ * This function locks (drm_exec_lock_obj()) objects that will be unmapped/
+ * remapped, and locks+prepares (drm_exec_prepare_object()) objects that
+ * will be newly mapped.
+ *
+ * The expected usage is:
+ *
+ *    vm_bind {
+ *        struct drm_exec exec;
+ *
+ *        // IGNORE_DUPLICATES is required, INTERRUPTIBLE_WAIT is recommended:
+ *        drm_exec_init(&exec, IGNORE_DUPLICATES | INTERRUPTIBLE_WAIT, 0);
+ *
+ *        drm_exec_until_all_locked (&exec) {
+ *            for_each_vm_bind_operation {
+ *                switch (op->op) {
+ *                case DRIVER_OP_UNMAP:
+ *                    ret = drm_gpuvm_sm_unmap_exec_lock(gpuvm, &exec, op->addr, op->range);
+ *                    break;
+ *                case DRIVER_OP_MAP:
+ *                    ret = drm_gpuvm_sm_map_exec_lock(gpuvm, &exec, num_fences,
+ *                                                     op->addr, op->range,
+ *                                                     obj, op->obj_offset);
+ *                    break;
+ *                }
+ *
+ *                drm_exec_retry_on_contention(&exec);
+ *                if (ret)
+ *                    return ret;
+ *            }
+ *        }
+ *    }
+ *
+ * This enables all locking to be performed before the driver begins modifying
+ * the VM.  This is safe to do in the case of overlapping DRIVER_VM_BIND_OPs,
+ * where an earlier op can alter the sequence of steps generated for a later
+ * op, because the later altered step will involve the same GEM object(s)
+ * already seen in the earlier locking step.  For example:
+ *
+ * 1) An earlier driver DRIVER_OP_UNMAP op removes the need for a
+ *    DRM_GPUVA_OP_REMAP/UNMAP step.  This is safe because we've already
+ *    locked the GEM object in the earlier DRIVER_OP_UNMAP op.
+ *
+ * 2) An earlier DRIVER_OP_MAP op overlaps with a later DRIVER_OP_MAP/UNMAP
+ *    op, introducing a DRM_GPUVA_OP_REMAP/UNMAP that wouldn't have been
+ *    required without the earlier DRIVER_OP_MAP.  This is safe because we've
+ *    already locked the GEM object in the earlier DRIVER_OP_MAP step.
+ *
+ * Returns: 0 on success or a negative error codec
+ */
+int
+drm_gpuvm_sm_map_exec_lock(struct drm_gpuvm *gpuvm,
+			   struct drm_exec *exec, unsigned int num_fences,
+			   u64 req_addr, u64 req_range,
+			   struct drm_gem_object *req_obj, u64 req_offset)
+{
+	if (req_obj) {
+		int ret = drm_exec_prepare_obj(exec, req_obj, num_fences);
+		if (ret)
+			return ret;
+	}
+
+	return __drm_gpuvm_sm_map(gpuvm, &lock_ops, exec,
+				  req_addr, req_range,
+				  req_obj, req_offset);
+
+}
+EXPORT_SYMBOL_GPL(drm_gpuvm_sm_map_exec_lock);
+
+/**
+ * drm_gpuvm_sm_unmap_exec_lock() - locks the objects touched by drm_gpuvm_sm_unmap()
+ * @gpuvm: the &drm_gpuvm representing the GPU VA space
+ * @exec: the &drm_exec locking context
+ * @req_addr: the start address of the range to unmap
+ * @req_range: the range of the mappings to unmap
+ *
+ * This function locks (drm_exec_lock_obj()) objects that will be unmapped/
+ * remapped by drm_gpuvm_sm_unmap().
+ *
+ * See drm_gpuvm_sm_map_exec_lock() for expected usage.
+ *
+ * Returns: 0 on success or a negative error code
+ */
+int
+drm_gpuvm_sm_unmap_exec_lock(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
+			     u64 req_addr, u64 req_range)
+{
+	return __drm_gpuvm_sm_unmap(gpuvm, &lock_ops, exec,
+				    req_addr, req_range);
+}
+EXPORT_SYMBOL_GPL(drm_gpuvm_sm_unmap_exec_lock);
+
 static struct drm_gpuva_op *
 gpuva_op_alloc(struct drm_gpuvm *gpuvm)
 {

include/drm/drm_gpuvm.h

@@ -1211,6 +1211,14 @@ int drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm, void *priv,
 int drm_gpuvm_sm_unmap(struct drm_gpuvm *gpuvm, void *priv,
 		       u64 addr, u64 range);
 
+int drm_gpuvm_sm_map_exec_lock(struct drm_gpuvm *gpuvm,
+			  struct drm_exec *exec, unsigned int num_fences,
+			  u64 req_addr, u64 req_range,
+			  struct drm_gem_object *obj, u64 offset);
+
+int drm_gpuvm_sm_unmap_exec_lock(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
+				 u64 req_addr, u64 req_range);
+
 void drm_gpuva_map(struct drm_gpuvm *gpuvm,
 		   struct drm_gpuva *va,
 		   struct drm_gpuva_op_map *op);