Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Baoquan He <bhe@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, mhocko@kernel.org, david@redhat.com,
        jgross@suse.com, akpm@linux-foundation.org, bhe@redhat.com
Subject: [Patch v2] mm/hotplug: Only respect mem= parameter during boot stage
Date:   Tue, 10 Dec 2019 16:44:13 +0800
Message-Id: <20191210084413.21957-1-bhe@redhat.com>
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In commit 357b4da50a62 ("x86: respect memory size limiting via mem=3D
parameter") a global varialbe global max_mem_size is added to store
the value parsed from 'mem=3D ', 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=3D ' parameter, it should be a restriction during
boot, but not impact the system memory adding/removing after booting.

  mem=3Dnn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
=09          ...

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=3D paramete=
r")
Signed-off-by: Baoquan He <bhe@redhat.com>
---
 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 s=
tart, u64 size)
 =09unsigned long flags =3D  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
 =09char *resource_name =3D "System RAM";
=20
-=09if (start + size > max_mem_size)
+=09/*
+=09 * Make sure value parsed from 'mem=3D' only restricts memory adding
+=09 * during boot-time, so that memory hotplug won't be impacted.
+=09 */
+=09if (start + size > max_mem_size && system_state < SYSTEM_RUNNING)
 =09=09return ERR_PTR(-E2BIG);
=20
 =09/*
--=20
2.17.2