[PATCH] mm/hotplug: Enable runtime update of memmap_on_memory parameter

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
This is dependent on patches posted at
https://lore.kernel.org/linux-mm/20230718024409.95742-1-aneesh.kumar@linux.ibm.com/

 mm/memory_hotplug.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6a8adbe030f9..21a5113fe9be 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -86,7 +86,12 @@ static int set_memmap_mode(const char *val, const struct kernel_param *kp)
 		mode =  MEMMAP_ON_MEMORY_DISABLE;
 
 matched:
+	/*
+	 * Avoid changing memmap mode during hotplug.
+	 */
+	get_online_mems();
 	*((int *)kp->arg) =  mode;
+	put_online_mems();
 	if (mode == MEMMAP_ON_MEMORY_FORCE) {
 		pr_info("Memory hotplug will reserve %ld pages in each memory block\n",
 			memory_block_align_base(memory_block_size_bytes()));
@@ -108,7 +113,7 @@ static const struct kernel_param_ops memmap_mode_ops = {
 	.set = set_memmap_mode,
 	.get = get_memmap_mode,
 };
-module_param_cb(memmap_on_memory, &memmap_mode_ops, &memmap_mode, 0444);
+module_param_cb(memmap_on_memory, &memmap_mode_ops, &memmap_mode, 0644);
 MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug\n"
 	"With value \"force\" it could result in memory wastage due to memmap size limitations \n"
 	"For example, if the memmap for a memory block requires 1 MiB, but the pageblock \n"
@@ -2162,18 +2167,16 @@ static int __ref try_remove_memory(u64 start, u64 size)
 	 * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
 	 * the same granularity it was added - a single memory block.
 	 */
-	if (mhp_memmap_on_memory()) {
-		ret = walk_memory_blocks(start, size, &mhp_altmap,
-					 get_vmemmap_altmap_cb);
-		if (ret) {
-			if (size != memory_block_size_bytes()) {
-				pr_warn("Refuse to remove %#llx - %#llx,"
-					"wrong granularity\n",
-					start, start + size);
-				return -EINVAL;
-			}
-			altmap = &mhp_altmap;
+	ret = walk_memory_blocks(start, size, &mhp_altmap,
+				 get_vmemmap_altmap_cb);
+	if (ret) {
+		if (size != memory_block_size_bytes()) {
+			pr_warn("Refuse to remove %#llx - %#llx,"
+				"wrong granularity\n",
+				start, start + size);
+			return -EINVAL;
 		}
+		altmap = &mhp_altmap;
 	}
 
 	/* remove memmap entry */
-- 
2.41.0