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 6e7c4762bd231eab3dc094c6ccd3c1ac8b2d21d1..d3be09092a3b54c019358841e8e1e1d8fc2175af 100644 (file)
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c
@@ -229,7 +229,7 @@ static inline int __pcilg_mio_inuser(
                :
                [cc] "+d" (cc), [val] "=d" (val), [len] "+d" (len),
                [dst] "+a" (dst), [cnt] "+d" (cnt), [tmp] "=d" (tmp),
-               [shift] "+d" (shift)
+               [shift] "+a" (shift)
                :
                [ioaddr] "a" (addr)
                : "cc", "memory");