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Fri, 11 Sep 2020 10:47:56 +0000 (UTC) Date: Fri, 11 Sep 2020 12:47:54 +0200 From: Cornelia Huck To: Collin Walling Subject: Re: [PATCH v5 6/8] s390/sclp: add extended-length sccb support for kvm guest Message-ID: <20200911124754.1a6c6cba.cohuck@redhat.com> In-Reply-To: <20200910093655.255774-7-walling@linux.ibm.com> References: <20200910093655.255774-1-walling@linux.ibm.com> <20200910093655.255774-7-walling@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=cohuck@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/11 03:28:41 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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, pbonzini@redhat.com, sumanthk@linux.ibm.com, mihajlov@linux.ibm.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 10 Sep 2020 05:36:53 -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 | 43 +++++++++++++++++++++++++---- > include/hw/s390x/sclp.h | 1 + > target/s390x/cpu_features_def.h.inc | 1 + > target/s390x/gen-features.c | 1 + > target/s390x/kvm.c | 8 ++++++ > 5 files changed, 48 insertions(+), 6 deletions(-) Acked-by: Cornelia Huck