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    Subject[PATCH 5.4 050/149] s390/ipl_parm: fix program check new psw handling
    Date
    From: Heiko Carstens <hca@linux.ibm.com>

    [ Upstream commit 88c2510cecb7e2b518e3c4fdf3cf0e13ebe9377c ]

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

    diff --git a/arch/s390/boot/ipl_parm.c b/arch/s390/boot/ipl_parm.c
    index 24ef67eb1cef..75905b548f69 100644
    --- a/arch/s390/boot/ipl_parm.c
    +++ b/arch/s390/boot/ipl_parm.c
    @@ -27,22 +27,25 @@ 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;
    }

    --
    2.30.2


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