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    Subject[PATCH AUTOSEL 5.4 45/63] s390/mem_detect: fix diag260() program check new psw handling
    Date
    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 62e7c13ce85c..032d68165216 100644
    --- a/arch/s390/boot/mem_detect.c
    +++ b/arch/s390/boot/mem_detect.c
    @@ -70,24 +70,27 @@ 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
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