s390/pci: Fix __pcilg_mio_inuser() inline assembly

commit c4abe6234246c75cdc43326415d9cff88b7cf06c upstream.

Use "a" constraint for the shift operand of the __pcilg_mio_inuser() inline
assembly. The used "d" constraint allows the compiler to use any general
purpose register for the shift operand, including register zero.

If register zero is used this my result in incorrect code generation:

 8f6:   a7 0a ff f8             ahi     %r0,-8
 8fa:   eb 32 00 00 00 0c       srlg    %r3,%r2,0  <----

If register zero is selected to contain the shift value, the srlg
instruction ignores the contents of the register and always shifts zero
bits. Therefore use the "a" constraint which does not permit to select
register zero.

Fixes: f058599e22d5 ("s390/pci: Fix s390_mmio_read/write with MIO")
Cc: stable@vger.kernel.org
Reported-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c
index 7e4cb95a431c9afd12b1311861c9bd61a77039da..ad500c22e812cbaa9bab277d6fafb2893cd1de5c 100644 (file)
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c
@@ -222,7 +222,7 @@ static inline int __pcilg_mio_inuser(
                [ioaddr_len] "+&d" (ioaddr_len.pair),
                [cc] "+d" (cc), [val] "=d" (val),
                [dst] "+a" (dst), [cnt] "+d" (cnt), [tmp] "=d" (tmp),
-               [shift] "+d" (shift)
+               [shift] "+a" (shift)
                :: "cc", "memory");
 
        /* did we write everything to the user space buffer? */