s390/ipl_parm: fix program check new psw handling

The __diag308() inline asm temporarily changes the program check new
psw to redirect a potential program check on the diag instruction.
Restoring of the program check new psw is done in C code behind the
inline asm.

This can be problematic, especially if the function is inlined, since
the compiler can reorder instructions in such a way that a different
instruction, which may result in a program check, might be executed
before the program check new psw has been restored.

To avoid such a scenario move restoring into the inline asm. For
consistency reasons move also saving of the original program check new
psw into the inline asm.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/boot/ipl_parm.c b/arch/s390/boot/ipl_parm.c
index bc1f973e656a0962a4bbf75d92d12971c8b95a80..6bf17c62377033d49b65b6a21f8110cbf066c4dd 100644 (file)
--- a/arch/s390/boot/ipl_parm.c
+++ b/arch/s390/boot/ipl_parm.c
@@ -28,22 +28,25 @@ static inline int __diag308(unsigned long subcode, void *addr)
        register unsigned long _addr asm("0") = (unsigned long)addr;
        register unsigned long _rc asm("1") = 0;
        unsigned long reg1, reg2;
-       psw_t old = S390_lowcore.program_new_psw;
+       psw_t old;
 
        asm volatile(
+               "       mvc     0(16,%[psw_old]),0(%[psw_pgm])\n"
                "       epsw    %0,%1\n"
-               "       st      %0,%[psw_pgm]\n"
-               "       st      %1,%[psw_pgm]+4\n"
+               "       st      %0,0(%[psw_pgm])\n"
+               "       st      %1,4(%[psw_pgm])\n"
                "       larl    %0,1f\n"
-               "       stg     %0,%[psw_pgm]+8\n"
+               "       stg     %0,8(%[psw_pgm])\n"
                "       diag    %[addr],%[subcode],0x308\n"
-               "1:     nopr    %%r7\n"
+               "1:     mvc     0(16,%[psw_pgm]),0(%[psw_old])\n"
                : "=&d" (reg1), "=&a" (reg2),
-                 [psw_pgm] "=Q" (S390_lowcore.program_new_psw),
+                 "+Q" (S390_lowcore.program_new_psw),
+                 "=Q" (old),
                  [addr] "+d" (_addr), "+d" (_rc)
-               : [subcode] "d" (subcode)
+               : [subcode] "d" (subcode),
+                 [psw_old] "a" (&old),
+                 [psw_pgm] "a" (&S390_lowcore.program_new_psw)
                : "cc", "memory");
-       S390_lowcore.program_new_psw = old;
        return _rc;
 }