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Wed, 15 Jul 2020 16:05:50 +0000 (UTC) Date: Wed, 15 Jul 2020 18:05:48 +0200 From: Cornelia Huck To: Collin Walling Subject: Re: [PATCH v4 6/8] s390/sclp: add extended-length sccb support for kvm guest Message-ID: <20200715180548.5ce11fcc.cohuck@redhat.com> In-Reply-To: References: <20200624202312.28349-1-walling@linux.ibm.com> <20200624202312.28349-7-walling@linux.ibm.com> <20200626120106.6ef7fddc.cohuck@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 02:01:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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 Wed, 15 Jul 2020 11:35:06 -0400 Collin Walling wrote: > 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. If we have the info, we might as well log it, I guess.