mm/memory_hotplug: replace an open-coded kmemdup() in add_memory_resource()

JIRA: https://issues.redhat.com/browse/RHEL-23824

commit 82b8a3b
Author: Vishal Verma <vishal.l.verma@intel.com>
Date:   Tue Nov 7 00:22:41 2023 -0700

    mm/memory_hotplug: replace an open-coded kmemdup() in add_memory_resource()
    
    Patch series "mm: use memmap_on_memory semantics for dax/kmem", v10.
    
    The dax/kmem driver can potentially hot-add large amounts of memory
    originating from CXL memory expanders, or NVDIMMs, or other 'device
    memories'.  There is a chance there isn't enough regular system memory
    available to fit the memmap for this new memory.  It's therefore
    desirable, if all other conditions are met, for the kmem managed memory to
    place its memmap on the newly added memory itself.
    
    The main hurdle for accomplishing this for kmem is that memmap_on_memory
    can only be done if the memory being added is equal to the size of one
    memblock.  To overcome this, allow the hotplug code to split an
    add_memory() request into memblock-sized chunks, and try_remove_memory()
    to also expect and handle such a scenario.
    
    Patch 1 replaces an open-coded kmemdup()
    
    Patch 2 teaches the memory_hotplug code to allow for splitting
    add_memory() and remove_memory() requests over memblock sized chunks.
    
    Patch 3 allows the dax region drivers to request memmap_on_memory
    semantics. CXL dax regions default this to 'on', all others default to
    off to keep existing behavior unchanged.
    
    
    This patch (of 3):
    
    A review of the memmap_on_memory modifications to add_memory_resource()
    revealed an instance of an open-coded kmemdup().  Replace it with
    kmemdup().
    
    Link: https://lkml.kernel.org/r/20231107-vv-kmem_memmap-v10-0-1253ec050ed0@intel.com
    Link: https://lkml.kernel.org/r/20231107-vv-kmem_memmap-v10-1-1253ec050ed0@intel.com
    Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
    Reviewed-by: David Hildenbrand <david@redhat.com>
    Reviewed-by: Fan Ni <fan.ni@samsung.com>
    Reported-by: Dan Williams <dan.j.williams@intel.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Oscar Salvador <osalvador@suse.de>
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Dave Jiang <dave.jiang@intel.com>
    Cc: "Huang, Ying" <ying.huang@intel.com>
    Cc: Jeff Moyer <jmoyer@redhat.com>
    Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

Author: JeffMoyer

mm/memory_hotplug.c

@@ -1475,13 +1475,13 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 	if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
 		if (mhp_supports_memmap_on_memory(size)) {
 			mhp_altmap.free = memory_block_memmap_on_memory_pages();
-			params.altmap = kmalloc(sizeof(struct vmem_altmap), GFP_KERNEL);
+			params.altmap = kmemdup(&mhp_altmap,
+						sizeof(struct vmem_altmap),
+						GFP_KERNEL);
 			if (!params.altmap) {
 				ret = -ENOMEM;
 				goto error;
 			}
-
-			memcpy(params.altmap, &mhp_altmap, sizeof(mhp_altmap));
 		}
 		/* fallback to not using altmap  */
 	}