[PATCH 5.13 123/351] s390/mem_detect: fix diag260() program check new psw handling

Greg Kroah-Hartman
2021-07-19T17:34:58Z

From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit 86807f348f418a84970eebb8f9912a7eea16b497 ]

The __diag260() 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/boot/mem_detect.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/s390/boot/mem_detect.c b/arch/s390/boot/mem_detect.c
index 40168e59abd3..3f093556dc3b 100644
--- a/arch/s390/boot/mem_detect.c
+++ b/arch/s390/boot/mem_detect.c
@@ -69,24 +69,27 @@ static int __diag260(unsigned long rx1, unsigned long rx2)
register unsigned long _ry asm("4") = 0x10; /* storage configuration */
int rc = -1; /* fail */
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 %[rx],%[ry],0x260\n"
" ipm %[rc]\n"
" srl %[rc],28\n"
- "1:\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),
[rc] "+&d" (rc), [ry] "+d" (_ry)
- : [rx] "d" (_rx1), "d" (_rx2)
+ : [rx] "d" (_rx1), "d" (_rx2),
+ [psw_old] "a" (&old),
+ [psw_pgm] "a" (&S390_lowcore.program_new_psw)
: "cc", "memory");
- S390_lowcore.program_new_psw = old;
return rc == 0 ? _ry : -1;
}

--
2.30.2