mm/memory_hotplug: Remove MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers were introduced
to prepare the transition of memory to and from a physically accessible
state. This enhancement was crucial for implementing the "memmap on memory"
feature for s390.

With introduction of dynamic (de)configuration of hotpluggable memory,
memory can be brought to accessible state before add_memory(). Memory
can be brought to inaccessible state before remove_memory(). Hence,
there is no need of MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory
notifiers anymore.

This basically reverts commit
c5f1e2d18909 ("mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers")
Additionally, apply minor adjustments to the function parameters of
move_pfn_range_to_zone() and mhp_supports_memmap_on_memory() to ensure
compatibility with the latest branch.

Acked-by: David Hildenbrand <[e-mail]>
Signed-off-by: Sumanth Korikkar <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

drivers/base/memory.c

···
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	unsigned long nr_vmemmap_pages = 0;
-	struct memory_notify arg;
 	struct zone *zone;
 	int ret;
 
···
 	if (mem->altmap)
 		nr_vmemmap_pages = mem->altmap->free;
 
-	arg.altmap_start_pfn = start_pfn;
-	arg.altmap_nr_pages = nr_vmemmap_pages;
-	arg.start_pfn = start_pfn + nr_vmemmap_pages;
-	arg.nr_pages = nr_pages - nr_vmemmap_pages;
 	mem_hotplug_begin();
-	ret = memory_notify(MEM_PREPARE_ONLINE, &arg);
-	ret = notifier_to_errno(ret);
-	if (ret)
-		goto out_notifier;
-
 	if (nr_vmemmap_pages) {
-		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages,
-						zone, mem->altmap->inaccessible);
+		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone);
 		if (ret)
 			goto out;
 	}
···
 					  nr_vmemmap_pages);
 
 	mem->zone = zone;
-	mem_hotplug_done();
-	return ret;
 out:
-	memory_notify(MEM_FINISH_OFFLINE, &arg);
-out_notifier:
 	mem_hotplug_done();
 	return ret;
 }
···
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	unsigned long nr_vmemmap_pages = 0;
-	struct memory_notify arg;
 	int ret;
 
 	if (!mem->zone)
···
 		mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
 
 	mem->zone = NULL;
-	arg.altmap_start_pfn = start_pfn;
-	arg.altmap_nr_pages = nr_vmemmap_pages;
-	arg.start_pfn = start_pfn + nr_vmemmap_pages;
-	arg.nr_pages = nr_pages - nr_vmemmap_pages;
-	memory_notify(MEM_FINISH_OFFLINE, &arg);
 out:
 	mem_hotplug_done();
 	return ret;

include/linux/memory.h

···
 #define	MEM_GOING_ONLINE	(1<<3)
 #define	MEM_CANCEL_ONLINE	(1<<4)
 #define	MEM_CANCEL_OFFLINE	(1<<5)
-#define	MEM_PREPARE_ONLINE	(1<<6)
-#define	MEM_FINISH_OFFLINE	(1<<7)
 
 struct memory_notify {
-	/*
-	 * The altmap_start_pfn and altmap_nr_pages fields are designated for
-	 * specifying the altmap range and are exclusively intended for use in
-	 * MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers.
-	 */
-	unsigned long altmap_start_pfn;
-	unsigned long altmap_nr_pages;
 	unsigned long start_pfn;
 	unsigned long nr_pages;
 };

include/linux/memory_hotplug.h

···
  * implies the node id (nid).
  */
 #define MHP_NID_IS_MGID		((__force mhp_t)BIT(2))
-/*
- * The hotplugged memory is completely inaccessible while the memory is
- * offline. The memory provider will handle MEM_PREPARE_ONLINE /
- * MEM_FINISH_OFFLINE notifications and make the memory accessible.
- *
- * This flag is only relevant when used along with MHP_MEMMAP_ON_MEMORY,
- * because the altmap cannot be written (e.g., poisoned) when adding
- * memory -- before it is set online.
- *
- * This allows for adding memory with an altmap that is not currently
- * made available by a hypervisor. When onlining that memory, the
- * hypervisor can be instructed to make that memory available, and
- * the onlining phase will not require any memory allocations, which is
- * helpful in low-memory situations.
- */
-#define MHP_OFFLINE_INACCESSIBLE	((__force mhp_t)BIT(3))
 
 /*
  * Extended parameters for memory hotplug:
···
 				      long nr_pages);
 /* VM interface that may be used by firmware interface */
 extern int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
-				     struct zone *zone, bool mhp_off_inaccessible);
+				     struct zone *zone);
 extern void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long nr_pages);
 extern int online_pages(unsigned long pfn, unsigned long nr_pages,
 			struct zone *zone, struct memory_group *group);

include/linux/memremap.h

···
 	unsigned long free;
 	unsigned long align;
 	unsigned long alloc;
-	bool inaccessible;
 };
 
 /*

mm/memory_hotplug.c

···
 }
 
 int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
-			      struct zone *zone, bool mhp_off_inaccessible)
+			      struct zone *zone)
 {
 	unsigned long end_pfn = pfn + nr_pages;
 	int ret, i;
···
 	ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
 	if (ret)
 		return ret;
-
-	/*
-	 * Memory block is accessible at this stage and hence poison the struct
-	 * pages now.  If the memory block is accessible during memory hotplug
-	 * addition phase, then page poisining is already performed in
-	 * sparse_add_section().
-	 */
-	if (mhp_off_inaccessible)
-		page_init_poison(pfn_to_page(pfn), sizeof(struct page) * nr_pages);
 
 	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE,
 			       false);
···
 }
 
 static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
-					    u64 start, u64 size, mhp_t mhp_flags)
+					    u64 start, u64 size)
 {
 	unsigned long memblock_size = memory_block_size_bytes();
 	u64 cur_start;
···
 		};
 
 		mhp_altmap.free = memory_block_memmap_on_memory_pages();
-		if (mhp_flags & MHP_OFFLINE_INACCESSIBLE)
-			mhp_altmap.inaccessible = true;
 		params.altmap = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
 					GFP_KERNEL);
 		if (!params.altmap) {
···
 	 */
 	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
 	    mhp_supports_memmap_on_memory()) {
-		ret = create_altmaps_and_memory_blocks(nid, group, start, size, mhp_flags);
+		ret = create_altmaps_and_memory_blocks(nid, group, start, size);
 		if (ret)
 			goto error;
 	} else {

mm/sparse.c

···
 	 * Poison uninitialized struct pages in order to catch invalid flags
 	 * combinations.
 	 */
-	if (!altmap || !altmap->inaccessible)
-		page_init_poison(memmap, sizeof(struct page) * nr_pages);
+	page_init_poison(memmap, sizeof(struct page) * nr_pages);
 
 	ms = __nr_to_section(section_nr);
 	set_section_nid(section_nr, nid);