s390/mem_detect: fix tprot() program check new psw handling

The tprot() 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/mem_detect.c b/arch/s390/boot/mem_detect.c
index 2c5a9c61b1013e0031cec6213b3642aa423cf404..4e17adbde4954d3ea177e293aa49f1ee963b63ac 100644 (file)
--- a/arch/s390/boot/mem_detect.c
+++ b/arch/s390/boot/mem_detect.c
@@ -118,24 +118,30 @@ static int diag260(void)
 
 static int tprot(unsigned long addr)
 {
-       unsigned long pgm_addr;
+       unsigned long reg1, reg2;
        int rc = -EFAULT;
-       psw_t old = S390_lowcore.program_new_psw;
+       psw_t old;
 
-       S390_lowcore.program_new_psw.mask = __extract_psw();
        asm volatile(
-               "       larl    %[pgm_addr],1f\n"
-               "       stg     %[pgm_addr],%[psw_pgm_addr]\n"
+               "       mvc     0(16,%[psw_old]),0(%[psw_pgm])\n"
+               "       epsw    %[reg1],%[reg2]\n"
+               "       st      %[reg1],0(%[psw_pgm])\n"
+               "       st      %[reg2],4(%[psw_pgm])\n"
+               "       larl    %[reg1],1f\n"
+               "       stg     %[reg1],8(%[psw_pgm])\n"
                "       tprot   0(%[addr]),0\n"
                "       ipm     %[rc]\n"
                "       srl     %[rc],28\n"
-               "1:\n"
-               : [pgm_addr] "=&d"(pgm_addr),
-                 [psw_pgm_addr] "=Q"(S390_lowcore.program_new_psw.addr),
-                 [rc] "+&d"(rc)
-               : [addr] "a"(addr)
+               "1:     mvc     0(16,%[psw_pgm]),0(%[psw_old])\n"
+               : [reg1] "=&d" (reg1),
+                 [reg2] "=&a" (reg2),
+                 [rc] "+&d" (rc),
+                 "=Q" (S390_lowcore.program_new_psw.addr),
+                 "=Q" (old)
+               : [psw_old] "a" (&old),
+                 [psw_pgm] "a" (&S390_lowcore.program_new_psw),
+                 [addr] "a" (addr)
                : "cc", "memory");
-       S390_lowcore.program_new_psw = old;
        return rc;
 }