[3.16.y-ckt stable] Patch "s390/hibernate: fix save and restore of kernel text section" 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/hibernate: fix save and restore of kernel text section

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 5d32cdce018ddacda45623b8ca06a106085be0e6 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens at de.ibm.com>
Date: Wed, 25 Mar 2015 10:13:33 +0100
Subject: s390/hibernate: fix save and restore of kernel text section

commit d74419495633493c9cd3f2bbeb7f3529d0edded6 upstream.

Sebastian reported a crash caused by a jump label mismatch after resume.
This happens because we do not save the kernel text section during suspend
and therefore also do not restore it during resume, but use the kernel image
that restores the old system.

This means that after a suspend/resume cycle we lost all modifications done
to the kernel text section.
The reason for this is the pfn_is_nosave() function, which incorrectly
returns that read-only pages don't need to be saved. This is incorrect since
we mark the kernel text section read-only.
We still need to make sure to not save and restore pages contained within
NSS and DCSS segment.
To fix this add an extra case for the kernel text section and only save
those pages if they are not contained within an NSS segment.

Fixes the following crash (and the above bugs as well):

Jump label code mismatch at netif_receive_skb_internal+0x28/0xd0
Found:    c0 04 00 00 00 00
Expected: c0 f4 00 00 00 11
New:      c0 04 00 00 00 00
Kernel panic - not syncing: Corrupted kernel text
CPU: 0 PID: 9 Comm: migration/0 Not tainted 3.19.0-01975-gb1b096e70f23 #4
Call Trace:
  [<0000000000113972>] show_stack+0x72/0xf0
  [<000000000081f15e>] dump_stack+0x6e/0x90
  [<000000000081c4e8>] panic+0x108/0x2b0
  [<000000000081be64>] jump_label_bug.isra.2+0x104/0x108
  [<0000000000112176>] __jump_label_transform+0x9e/0xd0
  [<00000000001121e6>] __sm_arch_jump_label_transform+0x3e/0x50
  [<00000000001d1136>] multi_cpu_stop+0x12e/0x170
  [<00000000001d1472>] cpu_stopper_thread+0xb2/0x168
  [<000000000015d2ac>] smpboot_thread_fn+0x134/0x1b0
  [<0000000000158baa>] kthread+0x10a/0x110
  [<0000000000824a86>] kernel_thread_starter+0x6/0xc

Reported-and-tested-by: Sebastian Ott <sebott at linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/s390/kernel/suspend.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/s390/kernel/suspend.c b/arch/s390/kernel/suspend.c
index 1c4c5accd220..d3236c9e226b 100644
--- a/arch/s390/kernel/suspend.c
+++ b/arch/s390/kernel/suspend.c
@@ -138,6 +138,8 @@ int pfn_is_nosave(unsigned long pfn)
 {
 	unsigned long nosave_begin_pfn = PFN_DOWN(__pa(&__nosave_begin));
 	unsigned long nosave_end_pfn = PFN_DOWN(__pa(&__nosave_end));
+	unsigned long eshared_pfn = PFN_DOWN(__pa(&_eshared)) - 1;
+	unsigned long stext_pfn = PFN_DOWN(__pa(&_stext));

 	/* Always save lowcore pages (LC protection might be enabled). */
 	if (pfn <= LC_PAGES)
@@ -145,6 +147,8 @@ int pfn_is_nosave(unsigned long pfn)
 	if (pfn >= nosave_begin_pfn && pfn < nosave_end_pfn)
 		return 1;
 	/* Skip memory holes and read-only pages (NSS, DCSS, ...). */
+	if (pfn >= stext_pfn && pfn <= eshared_pfn)
+		return ipl_info.type == IPL_TYPE_NSS ? 1 : 0;
 	if (tprot(PFN_PHYS(pfn)))
 		return 1;
 	return 0;