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-rw-r--r--Documentation/s390/vfio-ccw.rst6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/s390/vfio-ccw.rst b/Documentation/s390/vfio-ccw.rst
index fca9c4f5bd9c..23e7d136f8b4 100644
--- a/Documentation/s390/vfio-ccw.rst
+++ b/Documentation/s390/vfio-ccw.rst
@@ -335,6 +335,12 @@ device.
The current code allows the guest to start channel programs via
START SUBCHANNEL, and to issue HALT SUBCHANNEL and CLEAR SUBCHANNEL.
+Currently all channel programs are prefetched, regardless of the
+p-bit setting in the ORB. As a result, self modifying channel
+programs are not supported. For this reason, IPL has to be handled as
+a special case by a userspace/guest program; this has been implemented
+in QEMU's s390-ccw bios as of QEMU 4.1.
+
vfio-ccw supports classic (command mode) channel I/O only. Transport
mode (HPF) is not supported.