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s390/ipl_parm: fix program check new psw handling

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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>
This commit is contained in:
Heiko Carstens 2021-06-14 14:49:31 +02:00 committed by Vasily Gorbik
parent d66a4c7f76
commit 88c2510cec
1 changed files with 11 additions and 8 deletions
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19
arch/s390/boot/ipl_parm.c
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@ -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;
}