From 9a51c9ee6ca6610e4ab89945e6c75eda3a265ceb Mon Sep 17 00:00:00 2001 From: Halil Pasic Date: Thu, 24 May 2018 19:58:27 +0200 Subject: 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 Suggested-by: Dong Jia Shi Acked-by: Jason J. Herne Tested-by: Jason J. Herne Message-Id: <20180524175828.3143-2-pasic@linux.ibm.com> Signed-off-by: Cornelia Huck --- hw/s390x/css.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'hw/s390x/css.c') 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); -- cgit 1.4.1