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Wed, 15 Jul 2020 15:35:06 GMT Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D6D84124054; Wed, 15 Jul 2020 15:35:06 +0000 (GMT) Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9BB15124058; Wed, 15 Jul 2020 15:35:06 +0000 (GMT) Received: from localhost.localdomain (unknown [9.85.135.204]) by b01ledav002.gho.pok.ibm.com (Postfix) with ESMTPS; Wed, 15 Jul 2020 15:35:06 +0000 (GMT) Subject: Re: [PATCH v4 6/8] s390/sclp: add extended-length sccb support for kvm guest To: Cornelia Huck References: <20200624202312.28349-1-walling@linux.ibm.com> <20200624202312.28349-7-walling@linux.ibm.com> <20200626120106.6ef7fddc.cohuck@redhat.com> From: Collin Walling Message-ID: Date: Wed, 15 Jul 2020 11:35:06 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200626120106.6ef7fddc.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-15_12:2020-07-15, 2020-07-15 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 mlxlogscore=999 suspectscore=0 malwarescore=0 adultscore=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 spamscore=0 phishscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007150124 Received-SPF: pass client-ip=148.163.158.5; envelope-from=walling@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 09:18:04 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, 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: thuth@redhat.com, frankja@linux.ibm.com, mst@redhat.com, david@redhat.com, qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, svens@linux.ibm.com, pbonzini@redhat.com, mihajlov@linux.ibm.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/26/20 6:01 AM, Cornelia Huck wrote: > On Wed, 24 Jun 2020 16:23:10 -0400 > Collin Walling wrote: > >> As more features and facilities are added to the Read SCP Info (RSCPI) >> response, more space is required to store them. The space used to store >> these new features intrudes on the space originally used to store CPU >> entries. This means as more features and facilities are added to the >> RSCPI response, less space can be used to store CPU entries. >> >> With the Extended-Length SCCB (ELS) facility, a KVM guest can execute >> the RSCPI command and determine if the SCCB is large enough to store a >> complete reponse. If it is not large enough, then the required length >> will be set in the SCCB header. >> >> The caller of the SCLP command is responsible for creating a >> large-enough SCCB to store a complete response. Proper checking should >> be in place, and the caller should execute the command once-more with >> the large-enough SCCB. >> >> This facility also enables an extended SCCB for the Read CPU Info >> (RCPUI) command. >> >> When this facility is enabled, the boundary violation response cannot >> be a result from the RSCPI, RSCPI Forced, or RCPUI commands. >> >> In order to tolerate kernels that do not yet have full support for this >> feature, a "fixed" offset to the start of the CPU Entries within the >> Read SCP Info struct is set to allow for the original 248 max entries >> when this feature is disabled. >> >> Additionally, this is introduced as a CPU feature to protect the guest >> from migrating to a machine that does not support storing an extended >> SCCB. This could otherwise hinder the VM from being able to read all >> available CPU entries after migration (such as during re-ipl). >> >> Signed-off-by: Collin Walling >> --- >> hw/s390x/sclp.c | 24 +++++++++++++++++++++++- >> include/hw/s390x/sclp.h | 1 + >> target/s390x/cpu_features_def.inc.h | 1 + >> target/s390x/gen-features.c | 1 + >> target/s390x/kvm.c | 8 ++++++++ >> 5 files changed, 34 insertions(+), 1 deletion(-) >> > > (...) > >> @@ -111,6 +131,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb) >> CPUEntry *entries_start = (void *)sccb + offset_cpu; >> >> if (!sccb_verify_length(sccb, machine->possible_cpus->len, offset_cpu)) { >> + qemu_log_mask(LOG_GUEST_ERROR, "insufficient sccb size to store " >> + "read scp info response\n"); > > Not sure if logging needed/provided length would be helpful here. > I had the thought that it may be beneficial for kernel development -- it gives a response if an SCCB size needs to be larger. >> return; >> } >> > > (...) > > Acked-by: Cornelia Huck > Thanks. -- Regards, Collin Stay safe and stay healthy