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Thu, 19 Nov 2020 18:15:25 +0000 (GMT) Received: from cpe-66-24-58-13.stny.res.rr.com (unknown [9.85.152.80]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 19 Nov 2020 18:15:25 +0000 (GMT) Subject: Re: [PATCH v11 07/14] s390/vfio-ap: sysfs attribute to display the guest's matrix To: Halil Pasic Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@linux.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, mjrosato@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, fiuczy@linux.ibm.com, frankja@linux.ibm.com, david@redhat.com, hca@linux.ibm.com, gor@linux.ibm.com References: <20201022171209.19494-1-akrowiak@linux.ibm.com> <20201022171209.19494-8-akrowiak@linux.ibm.com> <20201028091758.73aa77a3.pasic@linux.ibm.com> <20201114001248.3b397c8c.pasic@linux.ibm.com> From: Tony Krowiak Message-ID: Date: Thu, 19 Nov 2020 13:15:25 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20201114001248.3b397c8c.pasic@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312,18.0.737 definitions=2020-11-19_09:2020-11-19,2020-11-19 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxlogscore=999 spamscore=0 impostorscore=0 mlxscore=0 adultscore=0 phishscore=0 clxscore=1015 lowpriorityscore=0 malwarescore=0 bulkscore=0 suspectscore=3 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011190125 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/13/20 6:12 PM, Halil Pasic wrote: > On Fri, 13 Nov 2020 12:27:32 -0500 > Tony Krowiak wrote: > >> >> On 10/28/20 4:17 AM, Halil Pasic wrote: >>> On Thu, 22 Oct 2020 13:12:02 -0400 >>> Tony Krowiak wrote: >>> >>>> +static ssize_t guest_matrix_show(struct device *dev, >>>> + struct device_attribute *attr, char *buf) >>>> +{ >>>> + ssize_t nchars; >>>> + struct mdev_device *mdev = mdev_from_dev(dev); >>>> + struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); >>>> + >>>> + if (!vfio_ap_mdev_has_crycb(matrix_mdev)) >>>> + return -ENODEV; >>> I'm wondering, would it make sense to have guest_matrix display the would >>> be guest matrix when we don't have a KVM? With the filtering in >>> place, the question in what guest_matrix would my (assign) matrix result >>> right now if I were to hook up my vfio_ap_mdev to a guest seems a >>> legitimate one. >> A couple of thoughts here: >> * The ENODEV informs the user that there is no guest running >>    which makes sense to me given this interface displays the >>    guest matrix. The alternative, which I considered, was to >>    display an empty matrix (i.e., nothing). >> * This would be a pretty drastic change to the design because >>    the shadow_apcb - which is what is displayed via this interface - is >>    only updated when the guest is started and while it is running (i.e., >>    hot plug of new adapters/domains). Making this change would >>    require changing that entire design concept which I am reluctant >>    to do at this point in the game. >> >> > No problem. My thinking was, that, because we can do the > assign/unassing ops also for the running guest, that we also have > the code to do the maintenance on the shadow_apcb. In this > series this code is conditional with respect to vfio_ap_mdev_has_crycb(). > E.g. > > static ssize_t assign_adapter_store(struct device *dev, > struct device_attribute *attr, > const char *buf, size_t count) > { > [..] > if (vfio_ap_mdev_has_crycb(matrix_mdev)) > if (vfio_ap_mdev_filter_guest_matrix(matrix_mdev, true)) > vfio_ap_mdev_commit_shadow_apcb(matrix_mdev); > > If one were to move the > vfio_ap_mdev_has_crycb() check into vfio_ap_mdev_commit_shadow_apcb() > then we would have an always up to date shatdow_apcb, we could display. > > I don't feel strongly about this. Was just an idea, because if the result > of the filtering is surprising, currently the only to see, without > knowing the algorithm, and possibly the state, and the history of the > system, is to actually start a guest. Okay, I can buy this and will make the change. > > Regards, > Halil >