[Patch v2] mm/hotplug: Only respect mem= parameter during boot stage

From: Baoquan He
Date: Tue Dec 10 2019 - 03:44:27 EST

In commit 357b4da50a62 ("x86: respect memory size limiting via mem=
parameter") a global varialbe global max_mem_size is added to store
the value parsed from 'mem= ', then checked when memory region is
added. This truly stops those DIMM from being added into system memory
during boot-time.

However, it also limits the later memory hotplug functionality. Any
memory board can't be hot added any more if its region is beyond the
max_mem_size. System will print error like below:

[ 216.387164] acpi PNP0C80:02: add_memory failed
[ 216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
[ 216.392187] acpi PNP0C80:02: Enumeration failure

>From document of 'mem= ' parameter, it should be a restriction during
boot, but not impact the system memory adding/removing after booting.

mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory

So fix it by also checking if it's during boot-time when restrict memory
adding. Otherwise, skip the restriction.

Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem= parameter")
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
mm/memory_hotplug.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 55ac23ef11c1..989707295d15 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -105,7 +105,11 @@ static struct resource *register_memory_resource(u64 start, u64 size)
char *resource_name = "System RAM";

- if (start + size > max_mem_size)
+ /*
+ * Make sure value parsed from 'mem=' only restricts memory adding
+ * during boot-time, so that memory hotplug won't be impacted.
+ */
+ if (start + size > max_mem_size && system_state < SYSTEM_RUNNING)
return ERR_PTR(-E2BIG);