This is a note to let you know that I've just added the patch titled
s390/boot/decompression: disable floating point in decompressor
to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
s390-boot-decompression-disable-floating-point-in-decompressor.patch
and it can be found in the queue-4.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From adc0b7fbf6fe9967505c0254d9535ec7288186ae Mon Sep 17 00:00:00 2001
From: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Date: Mon, 28 Sep 2015 22:47:42 +0200
Subject: s390/boot/decompression: disable floating point in decompressor
From: Christian Borntraeger <borntraeger@xxxxxxxxxx>
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@xxxxxxxxxx>
Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/boot/compressed/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/s390/boot/compressed/Makefile
+++ b/arch/s390/boot/compressed/Makefile
@@ -10,7 +10,7 @@ targets += misc.o piggy.o sizes.h head.o
KBUILD_CFLAGS := -m64 -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)
Patches currently in stable-queue which might be from borntraeger@xxxxxxxxxx are
queue-4.1/s390-boot-decompression-disable-floating-point-in-decompressor.patch
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