Currently, when adding memory, we create entries in /sys/firmware/memmap/
as "System RAM". This will lead to kexec-tools to add that memory to the
fixed-up initial memmap for a kexec kernel (loaded via kexec_load()). The
memory will be considered initial System RAM by the kexec'd kernel and
can no longer be reconfigured. This is not what happens during a real
reboot.
Let's add our memory via add_memory_driver_managed() now, so we won't
create entries in /sys/firmware/memmap/ and indicate the memory as
"System RAM (kmem)" in /proc/iomem. This allows everybody (especially
kexec-tools) to identify that this memory is special and has to be treated
differently than ordinary (hotplugged) System RAM.
Before configuring the namespace:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-33fffffff : namespace0.0
3280000000-32ffffffff : PCI Bus 0000:00
After configuring the namespace:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
148200000-33fffffff : dax0.0
3280000000-32ffffffff : PCI Bus 0000:00
After loading kmem before this change:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
150000000-33fffffff : dax0.0
150000000-33fffffff : System RAM
3280000000-32ffffffff : PCI Bus 0000:00
After loading kmem after this change:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
150000000-33fffffff : dax0.0
150000000-33fffffff : System RAM (kmem)
3280000000-32ffffffff : PCI Bus 0000:00
After a proper reboot:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
148200000-33fffffff : dax0.0
3280000000-32ffffffff : PCI Bus 0000:00
Within the kexec kernel before this change:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
150000000-33fffffff : System RAM
3280000000-32ffffffff : PCI Bus 0000:00
Within the kexec kernel after this change:
[root@localhost ~]# cat /proc/iomem
...
140000000-33fffffff : Persistent Memory
140000000-1481fffff : namespace0.0
148200000-33fffffff : dax0.0
3280000000-32ffffffff : PCI Bus 0000:00
/sys/firmware/memmap/ before this change:
0000000000000000-000000000009fc00 (System RAM)
000000000009fc00-00000000000a0000 (Reserved)
00000000000f0000-0000000000100000 (Reserved)
0000000000100000-00000000bffdf000 (System RAM)
00000000bffdf000-00000000c0000000 (Reserved)
00000000feffc000-00000000ff000000 (Reserved)
00000000fffc0000-0000000100000000 (Reserved)
0000000100000000-0000000140000000 (System RAM)
0000000150000000-0000000340000000 (System RAM)
/sys/firmware/memmap/ after a proper reboot:
0000000000000000-000000000009fc00 (System RAM)
000000000009fc00-00000000000a0000 (Reserved)
00000000000f0000-0000000000100000 (Reserved)
0000000000100000-00000000bffdf000 (System RAM)
00000000bffdf000-00000000c0000000 (Reserved)
00000000feffc000-00000000ff000000 (Reserved)
00000000fffc0000-0000000100000000 (Reserved)
0000000100000000-0000000140000000 (System RAM)
/sys/firmware/memmap/ after this change:
0000000000000000-000000000009fc00 (System RAM)
000000000009fc00-00000000000a0000 (Reserved)
00000000000f0000-0000000000100000 (Reserved)
0000000000100000-00000000bffdf000 (System RAM)
00000000bffdf000-00000000c0000000 (Reserved)
00000000feffc000-00000000ff000000 (Reserved)
00000000fffc0000-0000000100000000 (Reserved)
0000000100000000-0000000140000000 (System RAM)
kexec-tools already seem to basically ignore any System RAM that's not
on top level when searching for areas to place kexec images - but also
for determining crash areas to dump via kdump. Changing the resource name
won't have an impact.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
drivers/dax/kmem.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 3d0a7e702c94..5a645a24e359 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -65,7 +65,13 @@ int dev_dax_kmem_probe(struct device *dev)
new_res->flags = IORESOURCE_SYSTEM_RAM;
new_res->name = dev_name(dev);
- rc = add_memory(numa_node, new_res->start, resource_size(new_res));
+ /*
+ * Ensure that future kexec'd kernels will not treat this as RAM
+ * automatically.
+ */
+ rc = add_memory_driver_managed(numa_node, new_res->start,
+ resource_size(new_res),
+ "System RAM (kmem)");
if (rc) {
release_resource(new_res);
kfree(new_res);
--
2.25.3
