diff options
author | Halil Pasic <pasic@linux.ibm.com> | 2018-05-24 19:58:27 +0200 |
---|---|---|
committer | Cornelia Huck <cohuck@redhat.com> | 2018-06-18 10:50:32 +0200 |
commit | 9a51c9ee6ca6610e4ab89945e6c75eda3a265ceb (patch) | |
tree | a7ffc640ea034f56611d60fdba8d5e80f1d5b51f /hw/s390x | |
parent | 7a5342e7ccf2deb5553951024d57ec1327c926dd (diff) |
vfio-ccw: add force unlimited prefetch property
There is at least one guest (OS) such that although it does not rely on
the guarantees provided by ORB 1 word 9 bit (aka unlimited prefetch, aka
P bit) not being set, it fails to tell this to the machine.
Usually this ain't a big deal, as the original purpose of the P bit is to
allow for performance optimizations. vfio-ccw however can not provide the
guarantees required if the bit is not set.
It is not possible to implement support for the P bit not set without
transitioning to lower level protocols for vfio-ccw. So let's give the
user the opportunity to force setting the P bit, if the user knows this
is safe. For self modifying channel programs forcing the P bit is not
safe. If the P bit is forced for a self modifying channel program things
are expected to break in strange ways.
Let's also avoid warning multiple about P bit not set in the ORB in case
P bit is not told to be forced, and designate the affected vfio-ccw
device.
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Suggested-by: Dong Jia Shi <bjsdjshi@linux.ibm.com>
Acked-by: Jason J. Herne <jjherne@linux.ibm.com>
Tested-by: Jason J. Herne <jjherne@linux.ibm.com>
Message-Id: <20180524175828.3143-2-pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Diffstat (limited to 'hw/s390x')
-rw-r--r-- | hw/s390x/css.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/hw/s390x/css.c b/hw/s390x/css.c index 56c3fa8c89..39ae5bbf7e 100644 --- a/hw/s390x/css.c +++ b/hw/s390x/css.c @@ -1204,8 +1204,7 @@ static IOInstEnding sch_handle_start_func_passthrough(SubchDev *sch) * Only support prefetch enable mode. * Only support 64bit addressing idal. */ - if (!(orb->ctrl0 & ORB_CTRL0_MASK_PFCH) || - !(orb->ctrl0 & ORB_CTRL0_MASK_C64)) { + if (!(orb->ctrl0 & ORB_CTRL0_MASK_C64)) { warn_report("vfio-ccw requires PFCH and C64 flags set"); sch_gen_unit_exception(sch); css_inject_io_interrupt(sch); |