[PATCH v4 4/5] s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

[Sumanth Korikkar <sumanthk@linux.ibm.com>]

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.

Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 drivers/s390/char/sclp_cmd.c | 47 +++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index 355e63e44e95..c551dc6734fe 100644
--- a/drivers/s390/char/sclp_cmd.c
+++ b/drivers/s390/char/sclp_cmd.c
@@ -18,6 +18,7 @@
 #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>
@@ -26,6 +27,7 @@
 #include <asm/sclp.h>
 #include <asm/numa.h>
 #include <asm/facility.h>
+#include <asm/page-states.h>
 
 #include "sclp.h"
 
@@ -319,6 +321,7 @@ static bool contains_standby_increment(unsigned long start, unsigned long end)
 static int sclp_mem_notifier(struct notifier_block *nb,
 			     unsigned long action, void *data)
 {
+	unsigned long altmap_start, altmap_size;
 	unsigned long start, size;
 	struct memory_notify *arg;
 	unsigned char id;
@@ -340,13 +343,43 @@ static int sclp_mem_notifier(struct notifier_block *nb,
 		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_PREPARE_OFFLINE notifiers.
+		 */
+		altmap_start = arg->altmap_start_pfn << PAGE_SHIFT;
+		altmap_size = arg->altmap_nr_pages << PAGE_SHIFT;
+		/*
+		 * When altmap is in use, take the specified memory range
+		 * online, which includes the altmap.
+		 */
+		if (altmap_size) {
+			start = altmap_start;
+			size += altmap_size;
+		}
 		rc = sclp_mem_change_state(start, size, 1);
+		if (rc || !altmap_size)
+			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:
+		altmap_start = arg->altmap_start_pfn << PAGE_SHIFT;
+		altmap_size = arg->altmap_nr_pages << PAGE_SHIFT;
+		/*
+		 * When altmap is in use, take the specified memory range
+		 * offline, which includes the altmap.
+		 */
+		if (altmap_size) {
+			start = altmap_start;
+			size += altmap_size;
+		}
 		sclp_mem_change_state(start, size, 0);
 		break;
 	default:
@@ -397,7 +430,9 @@ static void __init add_memory_merged(u16 rn)
 	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;
-- 
2.41.0