From mboxrd@z Thu Jan 1 00:00:00 1970 From: Halil Pasic Date: Mon, 30 Jul 2018 14:18:21 +0000 Subject: Re: [PATCH v7 09/22] s390: vfio-ap: register matrix device with VFIO mdev framework Message-Id: In-Reply-To: <6a31797f-c8be-bb3d-c515-029ec52a56bf@linux.ibm.com> References: <6a31797f-c8be-bb3d-c515-029ec52a56bf@linux.ibm.com> To: linux-s390@vger.kernel.org, kvm@vger.kernel.org List-ID: On 07/30/2018 01:28 PM, Cornelia Huck wrote: > On Mon, 30 Jul 2018 13:24:24 +0200 > Pierre Morel wrote: > >> On 30/07/2018 11:49, Cornelia Huck wrote: >>> On Fri, 27 Jul 2018 16:17:47 +0200 >>> Halil Pasic wrote: >>> >>>> On 07/26/2018 09:54 PM, Christian Borntraeger wrote: >>>>> @@ -65,6 +66,21 @@ static int vfio_ap_matrix_dev_create(void) >>>>> { >>>>> int ret; >>>>> >>>>> + mutex_init(&matrix_dev.lock); >>>>> + INIT_LIST_HEAD(&matrix_dev.mdev_list); >>>>> + >>>>> + /* Test if PQAP(QCI) instruction is available */ >>>>> + if (test_facility(12)) { >>>>> + ret = ap_qci(&matrix_dev.info); >>>>> + if (ret && (ret != -EOPNOTSUPP)) { >>>> After Connie's curiosity was piqued I gave this another look. If >>>> I read the ap_qci() documentation and code correctly, it can return >>>> either 0 or -EOPNOTSUPP, but nothing else. So basically this >>>> is a dead branch. >>> Can it return -EOPNOTSUPP if facility 12 is present? >> >> I do not think it is reasonable to continue if >> we stated that facility 12 is present but the ap_qci function failed. >> >> So I propose that we return an error and break the insmod. > > So, would that be a bug? If yes, returning an error makes sense. > > (I can't check the documentation to find out about the interaction > between facility 12 and PQAP(QCI)...) If we are in z architectural mode and facility 12 is indicated and ap_qci() returns an error code, it's because of an exception while executing the PQAP instruction. The reason can be a bad input pointer or other stuff. It is likely a bug. I'm not sure how this interacts with machine checks though. I think we should report the problem and give up. > -- > To unsubscribe from this list: send the line "unsubscribe linux-s390" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >