On Mon, 2021-06-14 at 13:15 +0200, Cornelia Huck wrote: > On Fri, Jun 11 2021, Eric Farman <far...@linux.ibm.com> wrote: > > > The SCHIB.PMCW.CSENSE bit is used to determine whether the > > IRB should be set up with sense data, but that bit only > > indicates whether sense data is requested, not if it was > > provided by the device. For virtual devices, this is fine. > > > > For passthrough devices, hardware would present sense data > > in IRB.ECW, but that field is only valid if IRB.SCSW.E and > > IRB.ERW.S were also set. > > An important point is that IRB.ERW.S implies IRB.SCSW.E, I guess?
Correct. I can make this point more explicit so we don't have to reference the POPS to remind ourselves. > > If I parse the table regarding the ecw in the POP correctly, we might > also have model-dependent information stored, in which case we would > need to indicate zero sense data in the erw that we build. I wrestled with this. The best answer would be to pass the ERW from hardware via vfio-ccw back to QEMU, since that contains the "is this sense data or is this model-dependent info" bit (whatever that latter might be). ... > > > Let's only build the sense data in the IRB if the first byte > > of sense is nonzero (indicating it may have come from a virtual > > device), or the IRB.SCSW.E bit is already set (indicating it > > came from the hardware). That way, the guest driver can read > > the sense data if valid, or respond with a Sense CCW to get > > the sense data if it wants/needs. > > Hm, would it be possible that we get junk instead of proper sense > data > from the hardware, if IRB.ERW.S is not set? E.g. some residual > data. That would potentially trigger the first condition. > > Maybe we really need to special case virtual vs. passthrough devices > here. We can assume that a virtual device with a unit check always > has > proper sense data available. For passthrough devices, maybe we need > to > copy esw etc. from the irb we got hardware, and not try to construct > it > ourselves? ... Ah, I should read ahead. :) Yeah, that was where I was going to go above. I was considering that this would be a simpler solution near term, to get "normal" behavior behaving properly, but fixing it all in one go is probably better. Will see how bad a v3 cook starts looking. > > > Fixes: df1fe5bb4924 ("s390: Virtual channel subsystem support.") > > Fixes: 334e76850bbb ("vfio/ccw: update sense data if a unit check > > is pending") > > Signed-off-by: Eric Farman <far...@linux.ibm.com> > > --- > > > > Notes: > > v1->v2: > > - [MR] Add Fixes: tags > > - [CH] Reinstate the memcpy(sch->sense_data, irb.ecw) in > > vfio_ccw > > - [CH] Look at IRB.SCSW.E before copying sense into guest IRB > > > > v1: > > https://lore.kernel.org/qemu-devel/20210610202011.391029-1-far...@linux.ibm.com/ > > > > hw/s390x/css.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/hw/s390x/css.c b/hw/s390x/css.c > > index bed46f5ec3..8935f948d5 100644 > > --- a/hw/s390x/css.c > > +++ b/hw/s390x/css.c > > @@ -1659,9 +1659,15 @@ int css_do_tsch_get_irb(SubchDev *sch, IRB > > *target_irb, int *irb_len) > > } else { > > irb.esw[0] = 0x00800000; > > } > > - /* If a unit check is pending, copy sense data. */ > > + /* > > + * If a unit check is pending and concurrent sense > > + * is requested, copy the sense data if the sense > > + * data is plausibly valid. > > + */ > > if ((schib->scsw.dstat & SCSW_DSTAT_UNIT_CHECK) && > > - (schib->pmcw.chars & PMCW_CHARS_MASK_CSENSE)) { > > + (schib->pmcw.chars & PMCW_CHARS_MASK_CSENSE) && > > + ((schib->scsw.flags & SCSW_FLAGS_MASK_ECTL) || > > + (sch->sense_data[0] != 0))) { > > int i; > > > > irb.scsw.flags |= SCSW_FLAGS_MASK_ESWF | > > SCSW_FLAGS_MASK_ECTL; > > -- > > 2.25.1