linux-kernel - [PATCH 4/8] mm/memory_hotplug: return online type from add_memory_driver

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Message-ID: <20260114085201.3222597-5-gourry@gourry.net>
Date: Wed, 14 Jan 2026 03:51:56 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux.dev,
	kernel-team@...a.com,
	dan.j.williams@...el.com,
	vishal.l.verma@...el.com,
	dave.jiang@...el.com,
	david@...nel.org,
	mst@...hat.com,
	jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com,
	osalvador@...e.de,
	akpm@...ux-foundation.org
Subject: [PATCH 4/8] mm/memory_hotplug: return online type from add_memory_driver_managed()

Change add_memory_driver_managed() to return the online type (MMOP_*)
on success instead of 0. This allows callers to determine the actual
online state of the memory after addition, which is important when
MMOP_SYSTEM_DEFAULT is used and the actual online type depends on the
system default policy.

Update virtio_mem to handle the new return value semantics by checking
for rc < 0 to detect errors.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 drivers/dax/kmem.c          | 2 +-
 drivers/virtio/virtio_mem.c | 5 +++--
 mm/memory_hotplug.c         | 4 +++-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 5e0cf94a9620..d0dd36c536a0 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -178,7 +178,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 				range_len(&range), kmem_name, mhp_flags,
 				MMOP_SYSTEM_DEFAULT);
 
-		if (rc) {
+		if (rc < 0) {
 			dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
 					i, range.start, range.end);
 			remove_resource(res);
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index b1ec8f2b9e31..4decb44f5a43 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -656,15 +656,16 @@ static int virtio_mem_add_memory(struct virtio_mem *vm, uint64_t addr,
 	rc = add_memory_driver_managed(vm->mgid, addr, size, vm->resource_name,
 				       MHP_MERGE_RESOURCE | MHP_NID_IS_MGID,
 				       MMOP_SYSTEM_DEFAULT);
-	if (rc) {
+	if (rc < 0) {
 		atomic64_sub(size, &vm->offline_size);
 		dev_warn(&vm->vdev->dev, "adding memory failed: %d\n", rc);
 		/*
 		 * TODO: Linux MM does not properly clean up yet in all cases
 		 * where adding of memory failed - especially on -ENOMEM.
 		 */
+		return rc;
 	}
-	return rc;
+	return 0;
 }
 
 /*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 515ff9d18039..41974a1ccb91 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1689,7 +1689,7 @@ EXPORT_SYMBOL_GPL(add_memory);
  * MMOP_ONLINE_MOVABLE to online with that type, MMOP_OFFLINE to leave offline,
  * or MMOP_SYSTEM_DEFAULT to use the system default policy.
  *
- * Returns 0 on success, negative error code on failure.
+ * Returns the online type (MMOP_*) on success, negative error code on failure.
  */
 int add_memory_driver_managed(int nid, u64 start, u64 size,
 			      const char *resource_name, mhp_t mhp_flags,
@@ -1721,6 +1721,8 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
 	rc = __add_memory_resource(nid, res, mhp_flags, online_type);
 	if (rc < 0)
 		release_memory_resource(res);
+	else
+		rc = online_type;
 
 out_unlock:
 	unlock_device_hotplug();
-- 
2.52.0