3.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dominik Dingel <redacted>

commit ff1f3cb4b3ac5d039f02679f34cb1498d110d241 upstream.

The diagnose 500 subcode 3 contains the 32 bit subchannel id in bits 32-63
(counting from the left). As for other I/O instructions, bits 0-31 should be
ignored and thus not be passed to kvm_io_bus_write_cookie().

This fixes a bug where the guest passed non-zero bits 0-31 which the
host tried to interpret, leading to ioeventfd notification failures.

Signed-off-by: Dominik Dingel <redacted>
Reviewed-by: Cornelia Huck <redacted>
Signed-off-by: Cornelia Huck <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/kvm/diag.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c

@@ -122,7 +122,7 @@ static int __diag_virtio_hypercall(struc
 	 * - gpr 4 contains the index on the bus (optionally)
 	 */
 	ret = kvm_io_bus_write_cookie(vcpu->kvm, KVM_VIRTIO_CCW_NOTIFY_BUS,
-				      vcpu->run->s.regs.gprs[2],
+				      vcpu->run->s.regs.gprs[2] & 0xffffffff,
 				      8, &vcpu->run->s.regs.gprs[3],
 				      vcpu->run->s.regs.gprs[4]);
 	srcu_read_unlock(&vcpu->kvm->srcu, idx);