[PATCH v5 4/5] s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

Sumanth Korikkar
2023-11-28T15:52:52Z

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>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
drivers/s390/char/sclp_cmd.c | 41 ++++++++++++++++++++++++++++++------
1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index 355e63e44e95..7815e9bea69a 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"

@@ -340,13 +342,38 @@ 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_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:
@@ -397,7 +424,9 @@ 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;
--
2.40.1