Hi, this (RFC) is an initial stab at passing the halt and clear subchannel operations to the host device. Today, host userspace is emulating those two operations, but we really want to execute them on the host device (e.g. for error recovery situations).
The nice thing about this approach is that is independent from userspace changes: Unless userspace forwards halt/clear requests, we behave as before. Conversely, userspace can simply try to submit halt/clear, and old kernels will simply indicate that it is not supported. This survives triggering clear subchannel in the guest (hacked in by myself) together with an update QEMU (to be posted in a moment). Obviously, this needs some more work. Better support for async handling comes to mind. We probably also want to support other channel I/O instructions. Cornelia Huck (2): s390/cio: export hsch to modules vfio-ccw: support for halt/clear subchannel drivers/s390/cio/ioasm.c | 1 + drivers/s390/cio/vfio_ccw_drv.c | 10 ++++- drivers/s390/cio/vfio_ccw_fsm.c | 94 ++++++++++++++++++++++++++++++++++++----- 3 files changed, 93 insertions(+), 12 deletions(-) -- 2.14.3
