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Mon, 14 Jun 2021 13:03:03 +0000 (GMT) Received: from farman-thinkpad-t470p (unknown [9.160.30.100]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 14 Jun 2021 13:03:02 +0000 (GMT) Message-ID: <393c292444af5a43f8e020de411dd09842c7a9ca.camel@linux.ibm.com> Subject: Re: [PATCH v2] s390x/css: Selectively copy sense data to IRB From: Eric Farman To: Cornelia Huck , qemu-devel@nongnu.org, qemu-s390x@nongnu.org Date: Mon, 14 Jun 2021 09:03:02 -0400 In-Reply-To: <87sg1ky9x8.fsf@redhat.com> References: <20210611202151.615410-1-farman@linux.ibm.com> <87sg1ky9x8.fsf@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-16.el8) X-TM-AS-GCONF: 00 X-Proofpoint-GUID: AWemPfzLw_uETZIp4CZluD6KsPCYSTp7 X-Proofpoint-ORIG-GUID: 3DKl59tXKRT1PQ9fVdYFkJVWPI4SPSBM Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.761 definitions=2021-06-14_07:2021-06-14, 2021-06-14 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 adultscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 phishscore=0 malwarescore=0 mlxscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106140089 Received-SPF: pass client-ip=148.163.156.1; envelope-from=farman@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Matthew Rosato , David Hildenbrand , Richard Henderson , Halil Pasic , Christian Borntraeger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 2021-06-14 at 13:15 +0200, Cornelia Huck wrote: > On Fri, Jun 11 2021, Eric Farman 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 > > --- > > > > 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-farman@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