[PATCH v2 3/3] device-dax: Add system ram (add_memory()) with MHP_NO_FIRMWARE_MEMMAP

[David Hildenbrand <david@xxxxxxxxxx>]

Currently, when adding memory, we create entries in /sys/firmware/memmap/
as "System RAM". This does not reflect the reality and 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 kernel.

We should let the kexec kernel decide how to use that memory - just as
we do during an ordinary reboot.

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:
        [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 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. This behavior is not
changed by this patch. kexec-tools probably has to be fixed to also
include this memory in system dumps.

Note: kexec_file_load() does the right thing already within the kernel.

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 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index e159184e0ba0..929823a79816 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -65,7 +65,8 @@ 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), 0);
+       rc = add_memory(numa_node, new_res->start, resource_size(new_res),
+                       MHP_NO_FIRMWARE_MEMMAP);
        if (rc) {
                release_resource(new_res);
                kfree(new_res);
-- 
2.25.3