s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

MEM_PREPARE_ONLINE memory notifier makes memory block physical
accessible via sclp assign command. The notifier ensures self-contained
memory maps are accessible and hence enabling the "memmap on memory" on
s390.

MEM_FINISH_OFFLINE memory notifier shifts the memory block to an
inaccessible state via sclp unassign command.

Implementation considerations:
* When MHP_MEMMAP_ON_MEMORY is disabled, the system retains the old
behavior. This means the memory map is allocated from default memory.
* If MACHINE_HAS_EDAT1 is unavailable, MHP_MEMMAP_ON_MEMORY is
automatically disabled. This ensures that vmemmap pagetables do not
consume additional memory from the default memory allocator.
* The MEM_GOING_ONLINE notifier has been modified to perform no
operation, as MEM_PREPARE_ONLINE already executes the sclp assign
command.
* The MEM_CANCEL_ONLINE/MEM_OFFLINE notifier now performs no operation, as
MEM_FINISH_OFFLINE already executes the sclp unassign command.

Link: https://lkml.kernel.org/r/[e-mail]
Reviewed-by: Gerald Schaefer <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Signed-off-by: Sumanth Korikkar <[e-mail]>
Cc: Alexander Gordeev <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/s390/char/sclp_cmd.c

···
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/memory.h>
+#include <linux/memory_hotplug.h>
 #include <linux/module.h>
 #include <asm/ctlreg.h>
 #include <asm/chpid.h>
···
 #include <asm/sclp.h>
 #include <asm/numa.h>
 #include <asm/facility.h>
+#include <asm/page-states.h>
 
 #include "sclp.h"
 
···
 		if (contains_standby_increment(start, start + size))
 			rc = -EPERM;
 		break;
-	case MEM_GOING_ONLINE:
+	case MEM_PREPARE_ONLINE:
+		/*
+		 * Access the altmap_start_pfn and altmap_nr_pages fields
+		 * within the struct memory_notify specifically when dealing
+		 * with only MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers.
+		 *
+		 * When altmap is in use, take the specified memory range
+		 * online, which includes the altmap.
+		 */
+		if (arg->altmap_nr_pages) {
+			start = PFN_PHYS(arg->altmap_start_pfn);
+			size += PFN_PHYS(arg->altmap_nr_pages);
+		}
 		rc = sclp_mem_change_state(start, size, 1);
+		if (rc || !arg->altmap_nr_pages)
+			break;
+		/*
+		 * Set CMMA state to nodat here, since the struct page memory
+		 * at the beginning of the memory block will not go through the
+		 * buddy allocator later.
+		 */
+		__arch_set_page_nodat((void *)__va(start), arg->altmap_nr_pages);
 		break;
-	case MEM_CANCEL_ONLINE:
-		sclp_mem_change_state(start, size, 0);
-		break;
-	case MEM_OFFLINE:
+	case MEM_FINISH_OFFLINE:
+		/*
+		 * When altmap is in use, take the specified memory range
+		 * offline, which includes the altmap.
+		 */
+		if (arg->altmap_nr_pages) {
+			start = PFN_PHYS(arg->altmap_start_pfn);
+			size += PFN_PHYS(arg->altmap_nr_pages);
+		}
 		sclp_mem_change_state(start, size, 0);
 		break;
 	default:
···
 	if (!size)
 		goto skip_add;
 	for (addr = start; addr < start + size; addr += block_size)
-		add_memory(0, addr, block_size, MHP_NONE);
+		add_memory(0, addr, block_size,
+			   MACHINE_HAS_EDAT1 ?
+			   MHP_MEMMAP_ON_MEMORY | MHP_OFFLINE_INACCESSIBLE : MHP_NONE);
 skip_add:
 	first_rn = rn;
 	num = 1;