diff options
| author | Jared Rossi <jrossi@linux.ibm.com> | 2020-05-06 17:24:40 -0400 |
|---|---|---|
| committer | Cornelia Huck <cohuck@redhat.com> | 2020-06-02 13:14:08 +0200 |
| commit | 725b94d74128cd208bfdd446ad6b5f4b38cf5395 (patch) | |
| tree | 394d06fb3b404e9dc4e293fedaa4c18bc186049a /Documentation/s390 | |
| parent | e1750a3d9abbea2ece29cac8dc5a6f5bc19c1492 (diff) | |
vfio-ccw: Enable transparent CCW IPL from DASD
Remove the explicit prefetch check when using vfio-ccw devices.
This check does not trigger in practice as all Linux channel programs
are intended to use prefetch.
It is expected that all ORBs issued by Linux will request prefetch.
Although non-prefetching ORBs are not rejected, they will prefetch
nonetheless. A warning is issued up to once per 5 seconds when a
forced prefetch occurs.
A non-prefetch ORB does not necessarily result in an error, however
frequent encounters with non-prefetch ORBs indicate that channel
programs are being executed in a way that is inconsistent with what
the guest is requesting. While there is currently no known case of an
error caused by forced prefetch, it is possible in theory that forced
prefetch could result in an error if applied to a channel program that
is dependent on non-prefetch.
Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Message-Id: <20200506212440.31323-2-jrossi@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Diffstat (limited to 'Documentation/s390')
| -rw-r--r-- | Documentation/s390/vfio-ccw.rst | 6 |
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. |