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vfio-ccw: add force unlimited prefetch property

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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>
This commit is contained in:
Halil Pasic 2018-05-24 19:58:27 +02:00 • committed by Cornelia Huck
parent 7a5342e7cc
commit 9a51c9ee6c
2 changed files with 36 additions and 2 deletions
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3
hw/s390x/css.c
View file

@ -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);