s390/sclp: Add support for dynamic (de)configuration of memory

Provide a new interface for dynamic configuration and deconfiguration of
hotplug memory, allowing with/without memmap_on_memory support. It is a
follow up on the discussion with David when introducing memmap_on_memory
support for s390 and support dynamic (de)configuration of memory:
https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/
https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/

The original motivation for introducing memmap_on_memory on s390 was to
avoid using online memory to store struct pages metadata, particularly
for standby memory blocks. This became critical in cases where there was
an imbalance between standby and online memory, potentially leading to
boot failures due to insufficient memory for metadata allocation.

To address this, memmap_on_memory was utilized on s390. However, in its
current form, it adds struct pages metadata at the start of each memory
block at the time of addition and this configuration is static. It
cannot be changed at runtime. (When the user needs continuous physical
memory).

Inorder to provide more flexibility to the user and overcome the above
limitation, add option to dynamically configure and deconfigure
hotpluggable memory block with/without memmap_on_memory.

With the new interface, s390 will not add all possible hotplug memory in
advance, like before, to make it visible in sysfs for online/offline
actions. Instead, before memory block can be set online, it has to be
configured via a new interface in /sys/firmware/memory/memoryX/config,
which makes s390 similar to others.  i.e. Adding of hotpluggable memory is
controlled by the user instead of adding it at boottime.

The s390 kernel sysfs interface to configure and deconfigure memory is
as follows (considering the upcoming lsmem changes):

* Initial memory layout:
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

* Configure memory
sys="/sys"
echo 1 > $sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff    2G  online  0-15  yes        no
0x80000000-0x87ffffff  128M offline    16  yes        yes
0x88000000-0xffffffff  1.9G offline 17-31  no         yes

* Deconfigure memory
echo 0 > $sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

3. Enable memmap_on_memory and online it.
echo 0 > $sys/devices/system/memory/memory5/online
echo 0 > $sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         no
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

echo 1 > $sys/firmware/memory/memory5/memmap_on_memory
echo 1 > $sys/firmware/memory/memory5/config
echo 1 > $sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online  0-4   yes        no
0x28000000-0x2fffffff  128M  online  5     yes        yes
0x30000000-0x7fffffff  1.3G  online  6-15  yes        no
0x80000000-0xffffffff    2G  offline 16-31 no         yes

4. Disable memmap_on_memory and online it.
echo 0 > $sys/devices/system/memory/memory5/online
echo 0 > $sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         yes
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

echo 0 > $sys/firmware/memory/memory5/memmap_on_memory
echo 1 > $sys/firmware/memory/memory5/config
echo 1 > $sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff  2G    online  0-15  yes        no
0x80000000-0xffffffff  2G    offline 16-31 no         yes

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

0 files changed, 0 insertions, 0 deletions