[3.16.y-ckt stable] Patch "s390/boot/decompression: disable floating point in decompressor" 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/boot/decompression: disable floating point in decompressor

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-ckt20.

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 8383fc115adcce4839fbc2f58efbaf4133408bcd Mon Sep 17 00:00:00 2001
From: Christian Borntraeger <borntraeger at de.ibm.com>
Date: Mon, 28 Sep 2015 22:47:42 +0200
Subject: s390/boot/decompression: disable floating point in decompressor

commit adc0b7fbf6fe9967505c0254d9535ec7288186ae upstream.

my gcc 5.1 used an ldgr instruction with a register != 0,2,4,6 for
spilling/filling into a floating point register in our decompressor.

This will cause an AFP-register data exception as the decompressor
did not setup the additional floating point registers via cr0.
That causes a program check loop that looked like a hang with
one "Uncompressing Linux... " message (directly booted via kvm)
or a loop of "Uncompressing Linux... " messages (when booted via
zipl boot loader).

The offending code in my build was

   48e400:       e3 c0 af ff ff 71       lay     %r12,-1(%r10)
-->48e406:       b3 c1 00 1c             ldgr    %f1,%r12
   48e40a:       ec 6c 01 22 02 7f       clij    %r6,2,12,0x48e64e

but gcc could do spilling into an fpr at any function. We can
simply disable floating point support at that early stage.

Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/s390/boot/compressed/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
index f90d1fc6d603..f70b2321071e 100644
--- a/arch/s390/boot/compressed/Makefile
+++ b/arch/s390/boot/compressed/Makefile
@@ -12,7 +12,7 @@ targets += misc.o piggy.o sizes.h head$(BITS).o

 KBUILD_CFLAGS := -m$(BITS) -D__KERNEL__ $(LINUX_INCLUDE) -O2
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
-KBUILD_CFLAGS += $(cflags-y) -fno-delete-null-pointer-checks
+KBUILD_CFLAGS += $(cflags-y) -fno-delete-null-pointer-checks -msoft-float
 KBUILD_CFLAGS += $(call cc-option,-mpacked-stack)
 KBUILD_CFLAGS += $(call cc-option,-ffreestanding)