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 a90499c087f0c5e917c1f36072f56c0979951d1a..2ee7b5a5016c7d415fa6904974f31c376b1c4e43 100644 (file)
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c
@@ -223,7 +223,7 @@ 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? */