[PATCH v7 7/7] mm/memory_hotplug: Enable runtime update of memmap_on_memory parameter

[Aneesh Kumar K.V]

Allow updating memmap_on_memory mode after the kernel boot. Memory
hotplug done after the mode update will use the new mmemap_on_memory
value.

Acked-by: David Hildenbrand <da...@redhat.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
 mm/memory_hotplug.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1ce8ad04a980..d282664f558e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -89,7 +89,10 @@ static int set_memmap_mode(const char *val, const struct 
kernel_param *kp)
                else
                        mode = MEMMAP_ON_MEMORY_DISABLE;
        }
+       /* Avoid changing memmap mode during hotplug. */
+       get_online_mems();
        *((int *)kp->arg) = mode;
+       put_online_mems();
        if (mode == MEMMAP_ON_MEMORY_FORCE) {
                unsigned long memmap_pages = 
memory_block_memmap_on_memory_pages();
 
@@ -110,7 +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 (Y/N/force)");
@@ -2172,22 +2175,20 @@ 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, &mem, test_has_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 = mem->altmap;
-                       /*
-                        * Mark altmap NULL so that we can add a debug
-                        * check on memblock free.
-                        */
-                       mem->altmap = NULL;
+       ret = walk_memory_blocks(start, size, &mem, test_has_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 = mem->altmap;
+               /*
+                * Mark altmap NULL so that we can add a debug
+                * check on memblock free.
+                */
+               mem->altmap = NULL;
        }
 
        /* remove memmap entry */
-- 
2.41.0