s390/cpumf: Fix lpp detection

we have to check bit 40 of the facility list before issuing LPP
and not bit 48. Otherwise a guest running on a system with
"The decimal-floating-point zoned-conversion facility" and without
the "The set-program-parameters facility" might crash on an lpp
instruction.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: stable@vger.kernel.org # v4.4+
Fixes: e22cf8ca6f75 ("s390/cpumf: rework program parameter setting to detect guest samples")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S
index c5febe84eba633385cd7a8c09bee87e484c2e05c..03c2b469c4725172e4c6750cb8bcb0fb4edea075 100644 (file)
--- a/arch/s390/kernel/head64.S
+++ b/arch/s390/kernel/head64.S
@@ -16,7 +16,7 @@
 
 __HEAD
 ENTRY(startup_continue)
-       tm      __LC_STFLE_FAC_LIST+6,0x80      # LPP available ?
+       tm      __LC_STFLE_FAC_LIST+5,0x80      # LPP available ?
        jz      0f
        xc      __LC_LPP+1(7,0),__LC_LPP+1      # clear lpp and current_pid
        mvi     __LC_LPP,0x80                   #   and set LPP_MAGIC