4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
[ Upstream commit e991c24d68b8c0ba297eeb7af80b1e398e98c33f ]
We have quite a lot of code that depends on the order of the
__ctl_load inline assemby and subsequent memory accesses, like
e.g. disabling lowcore protection and the writing to lowcore.
Since the __ctl_load macro does not have memory barrier semantics, nor
any other dependencies the compiler is, theoretically, free to shuffle
code around. Or in other words: storing to lowcore could happen before
lowcore protection is disabled.
In order to avoid this class of potential bugs simply add a full
memory barrier to the __ctl_load macro.
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/include/asm/ctl_reg.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/s390/include/asm/ctl_reg.h
+++ b/arch/s390/include/asm/ctl_reg.h
@@ -15,7 +15,9 @@
BUILD_BUG_ON(sizeof(addrtype) != (high - low + 1) * sizeof(long));\
asm volatile( \
" lctlg %1,%2,%0\n" \
- : : "Q" (*(addrtype *)(&array)), "i" (low), "i" (high));\
+ : \
+ : "Q" (*(addrtype *)(&array)), "i" (low), "i" (high) \
+ : "memory"); \
}
#define __ctl_store(array, low, high) { \