[PATCH] virtio-ccw: diag 500 may return a negative cookie

[Cornelia Huck <cohuck@redhat.com>]

If something goes wrong in the kvm io bus handling, the virtio-ccw
diagnose may return a negative error value in the cookie gpr.

Document this.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---

Even if the virtio spec is the correct place to specify what diag 500
subcode 3 does, we also should mention here that the cookie may be
an error.

---
 Documentation/virtual/kvm/s390-diag.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/s390-diag.txt b/Documentation/virtual/kvm/s390-diag.txt
index 48c4921794ed..7c52e5f8b210 100644
--- a/Documentation/virtual/kvm/s390-diag.txt
+++ b/Documentation/virtual/kvm/s390-diag.txt
@@ -68,7 +68,8 @@ Subcode 3 - virtio-ccw notification
     identifier, it is ignored.
 
     After completion of the DIAGNOSE call, general register 2 may contain
-    a 64bit identifier (in the kvm_io_bus cookie case).
+    a 64bit identifier (in the kvm_io_bus cookie case), or a negative
+    error value, if an internal error occurred.
 
     See also the virtio standard for a discussion of this hypercall.
 
-- 
2.17.2