s390/ctl_reg: make __ctl_load a full memory barrier

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@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/s390/include/asm/ctl_reg.h b/arch/s390/include/asm/ctl_reg.h
index d7697ab802f6..8e136b88cdf4 100644
--- 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) {                                 \