[ 3.5.y.z extended stable ] Patch "s390/memory hotplug: prevent offline of active memory" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    s390/memory hotplug: prevent offline of active memory

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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>From 7adb147da53c4f2ff4a8915091d8c2d25fe1f4a4 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens at de.ibm.com>
Date: Thu, 25 Apr 2013 10:03:15 +0200
Subject: [PATCH] s390/memory hotplug: prevent offline of active memory
 increments

commit 94c163663fc1dcfc067a5fb3cc1446b9469975ce upstream.

In case a machine supports memory hotplug all active memory increments
present at IPL time have been initialized with a "usecount" of 1.
This is wrong if the memory increment size is larger than the memory
section size of the memory hotplug code. If that is the case the
usecount must be initialized with the number of memory sections that
fit into one memory increment.
Otherwise it is possible to put a memory increment into standby state
even if there are still active sections.
Afterwards addressing exceptions might happen which cause the kernel
to panic.
However even worse, if a memory increment was put into standby state
and afterwards into active state again, it's contents would have been
zeroed, leading to memory corruption.

This was only an issue for machines that support standby memory and
have at least 256GB memory.

This is broken since commit fdb1bb15 "[S390] sclp/memory hotplug: fix
initial usecount of increments".

Signed-off-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer at de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/s390/char/sclp_cmd.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index 766cb7b..1845ab5 100644
--- a/drivers/s390/char/sclp_cmd.c
+++ b/drivers/s390/char/sclp_cmd.c
@@ -529,6 +529,8 @@ static void __init sclp_add_standby_memory(void)
 	add_memory_merged(0);
 }

+#define MEM_SCT_SIZE (1UL << SECTION_SIZE_BITS)
+
 static void __init insert_increment(u16 rn, int standby, int assigned)
 {
 	struct memory_increment *incr, *new_incr;
@@ -541,7 +543,7 @@ static void __init insert_increment(u16 rn, int standby, int assigned)
 	new_incr->rn = rn;
 	new_incr->standby = standby;
 	if (!standby)
-		new_incr->usecount = 1;
+		new_incr->usecount = rzm > MEM_SCT_SIZE ? rzm/MEM_SCT_SIZE : 1;
 	last_rn = 0;
 	prev = &sclp_mem_list;
 	list_for_each_entry(incr, &sclp_mem_list, list) {
--
1.8.1.2