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    Subject[PATCH 5.13 124/351] s390/mem_detect: fix tprot() program check new psw handling
    Date
    From: Heiko Carstens <hca@linux.ibm.com>

    [ Upstream commit da9057576785aaab52e706e76c0475c85b77ec14 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/s390/boot/mem_detect.c | 28 +++++++++++++++++-----------
    1 file changed, 17 insertions(+), 11 deletions(-)

    diff --git a/arch/s390/boot/mem_detect.c b/arch/s390/boot/mem_detect.c
    index 3f093556dc3b..a0e980f57c02 100644
    --- a/arch/s390/boot/mem_detect.c
    +++ b/arch/s390/boot/mem_detect.c
    @@ -114,24 +114,30 @@ 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;
    }

    --
    2.30.2


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