[PATCH v4 4/9] mm/memory_hotplug: add __add_memory_driver_managed() with online_type arg

[Gregory Price]

Existing callers of add_memory_driver_managed cannot select the
preferred online type (ZONE_NORMAL vs ZONE_MOVABLE), requiring it to
hot-add memory as offline blocks, and then follow up by onlining each
memory block individually.

Most drivers prefer the system default, but the CXL driver wants to
plumb a preferred policy through the dax kmem driver.

Refactor APIs to add a new interface which allows the dax kmem module
to select a preferred policy.

Overriding the configured auto-online policy is only safe for known
in-tree modules, where we know the override reflects a different,
user-requested policy.  We do not want arbitrary out-of-tree drivers
silently overriding the system-wide onlining policy, so restrict the
new interface to the kmem module using EXPORT_SYMBOL_FOR_MODULES()
rather than a plain EXPORT_SYMBOL_GPL().  Other in-tree modules (e.g.
cxl_core) can be added to the allowed list as the need arises.

Refactor add_memory_driver_managed, extract __add_memory_driver_managed
- Add proper kernel-doc for add_memory_driver_managed while refactoring
- New helper accepts an explicit online_type.
- New helper validates online_type is between OFFLINE and ONLINE_MOVABLE

Refactor: add_memory_resource, extract __add_memory_resource
- new helper accepts an explicit online_type

Original APIs now explicitly pass the system-default to new helpers.

No functional change for existing users.

Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
 include/linux/memory_hotplug.h |  3 ++
 mm/memory_hotplug.c            | 61 +++++++++++++++++++++++++++++-----
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index f059025f8f8b..d3edeb80aadb 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -294,6 +294,9 @@ extern int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
 extern int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
 extern int add_memory_resource(int nid, struct resource *resource,
 			       mhp_t mhp_flags);
+int __add_memory_driver_managed(int nid, u64 start, u64 size,
+				const char *resource_name, mhp_t mhp_flags,
+				enum mmop online_type);
 extern int add_memory_driver_managed(int nid, u64 start, u64 size,
 				     const char *resource_name,
 				     mhp_t mhp_flags);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 494257054095..7d145217adc6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1494,10 +1494,10 @@ static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
  *
  * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
  */
-int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
+static int __add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags,
+				 enum mmop online_type)
 {
 	struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
-	enum mmop online_type = mhp_get_default_online_type();
 	enum memblock_flags memblock_flags = MEMBLOCK_NONE;
 	struct memory_group *group = NULL;
 	u64 start, size;
@@ -1585,7 +1585,7 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 		merge_system_ram_resource(res);
 
 	/* online pages if requested */
-	if (mhp_get_default_online_type() != MMOP_OFFLINE)
+	if (online_type != MMOP_OFFLINE)
 		walk_memory_blocks(start, size, &online_type,
 				   online_memory_block);
 
@@ -1603,7 +1603,13 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 	return ret;
 }
 
-/* requires device_hotplug_lock, see add_memory_resource() */
+int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
+{
+	return __add_memory_resource(nid, res, mhp_flags,
+				     mhp_get_default_online_type());
+}
+
+/* requires device_hotplug_lock, see __add_memory_resource() */
 int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
 {
 	struct resource *res;
@@ -1631,7 +1637,15 @@ int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
 }
 EXPORT_SYMBOL_GPL(add_memory);
 
-/*
+/**
+ * __add_memory_driver_managed - add driver-managed memory with explicit online_type
+ * @nid: NUMA node ID where the memory will be added
+ * @start: Start physical address of the memory range
+ * @size: Size of the memory range in bytes
+ * @resource_name: Resource name in format "System RAM ($DRIVER)"
+ * @mhp_flags: Memory hotplug flags
+ * @online_type: Auto-Online behavior (offline, online, kernel, movable)
+ *
  * Add special, driver-managed memory to the system as system RAM. Such
  * memory is not exposed via the raw firmware-provided memmap as system
  * RAM, instead, it is detected and added by a driver - during cold boot,
@@ -1639,6 +1653,7 @@ EXPORT_SYMBOL_GPL(add_memory);
  *
  * Reasons why this memory should not be used for the initial memmap of a
  * kexec kernel or for placing kexec images:
+ *
  * - The booting kernel is in charge of determining how this memory will be
  *   used (e.g., use persistent memory as system RAM)
  * - Coordination with a hypervisor is required before this memory
@@ -1651,9 +1666,12 @@ EXPORT_SYMBOL_GPL(add_memory);
  *
  * The resource_name (visible via /proc/iomem) has to have the format
  * "System RAM ($DRIVER)".
+ *
+ * Return: 0 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)
+int __add_memory_driver_managed(int nid, u64 start, u64 size,
+				const char *resource_name, mhp_t mhp_flags,
+				enum mmop online_type)
 {
 	struct resource *res;
 	int rc;
@@ -1663,6 +1681,9 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
 	    resource_name[strlen(resource_name) - 1] != ')')
 		return -EINVAL;
 
+	if (online_type < MMOP_OFFLINE || online_type > MMOP_ONLINE_MOVABLE)
+		return -EINVAL;
+
 	lock_device_hotplug();
 
 	res = register_memory_resource(start, size, resource_name);
@@ -1671,7 +1692,7 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
 		goto out_unlock;
 	}
 
-	rc = add_memory_resource(nid, res, mhp_flags);
+	rc = __add_memory_resource(nid, res, mhp_flags, online_type);
 	if (rc < 0)
 		release_memory_resource(res);
 
@@ -1679,6 +1700,30 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
 	unlock_device_hotplug();
 	return rc;
 }
+EXPORT_SYMBOL_FOR_MODULES(__add_memory_driver_managed, "kmem");
+
+/**
+ * add_memory_driver_managed - add driver-managed memory
+ * @nid: NUMA node ID where the memory will be added
+ * @start: Start physical address of the memory range
+ * @size: Size of the memory range in bytes
+ * @resource_name: Resource name in format "System RAM ($DRIVER)"
+ * @mhp_flags: Memory hotplug flags
+ *
+ * Add driver-managed memory with the system default online type set by
+ * build config or kernel boot parameter.
+ *
+ * See __add_memory_driver_managed for more details.
+ *
+ * Return: 0 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)
+{
+	return __add_memory_driver_managed(nid, start, size, resource_name,
+					   mhp_flags,
+					   mhp_get_default_online_type());
+}
 EXPORT_SYMBOL_GPL(add_memory_driver_managed);
 
 /*
-- 
2.54.0