[3.16.y-ckt stable] Patch "s390/sclp: clear upper register halves in _sclp_print_early" 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/sclp: clear upper register halves in _sclp_print_early

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-ckt16.

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 402930e89850ad4b44642b5552a1bfacd5299900 Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidefsky at de.ibm.com>
Date: Mon, 6 Jul 2015 17:58:19 +0200
Subject: s390/sclp: clear upper register halves in _sclp_print_early

commit f9c87a6f46d508eae0d9ae640be98d50f237f827 upstream.

If the kernel is compiled with gcc 5.1 and the XZ compression option
the decompress_kernel function calls _sclp_print_early in 64-bit mode
while the content of the upper register half of %r6 is non-zero.
This causes a specification exception on the servc instruction in
_sclp_servc.

The _sclp_print_early function saves and restores the upper registers
halves but it fails to clear them for the 31-bit code of the mini sclp
driver.

Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/s390/kernel/sclp.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/s390/kernel/sclp.S b/arch/s390/kernel/sclp.S
index a41f2c99dcc8..a0c4e7652647 100644
--- a/arch/s390/kernel/sclp.S
+++ b/arch/s390/kernel/sclp.S
@@ -277,6 +277,8 @@ ENTRY(_sclp_print_early)
 	jno	.Lesa2
 	ahi	%r15,-80
 	stmh	%r6,%r15,96(%r15)		# store upper register halves
+	basr	%r13,0
+	lmh	%r0,%r15,.Lzeroes-.(%r13)	# clear upper register halves
 .Lesa2:
 #endif
 	lr	%r10,%r2			# save string pointer
@@ -300,6 +302,8 @@ ENTRY(_sclp_print_early)
 #endif
 	lm	%r6,%r15,120(%r15)		# restore registers
 	br	%r14
+.Lzeroes:
+	.fill	64,4,0

 .LwritedataS4:
 	.long	0x00760005			# SCLP command for write data