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

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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>
This commit is contained in:
Heiko Carstens 2021-06-14 22:09:20 +02:00 committed by Vasily Gorbik
parent 1b2f281f45
commit da90575767
1 changed files with 17 additions and 11 deletions
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28
arch/s390/boot/mem_detect.c
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@ -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;
}