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Wed, 24 Jun 2020 14:57:33 +0000 (UTC) Date: Wed, 24 Jun 2020 16:57:30 +0200 From: Cornelia Huck To: Collin Walling Subject: Re: [PATCH v3 6/8] s390/sclp: add extended-length sccb support for kvm guest Message-ID: <20200624165730.358a883f.cohuck@redhat.com> In-Reply-To: <7ad94e6b-7e5e-04f6-109a-990075a1d8c2@linux.ibm.com> References: <20200618222258.23287-1-walling@linux.ibm.com> <20200618222258.23287-7-walling@linux.ibm.com> <20200624143635.2d87c1ca.cohuck@redhat.com> <20200624145500.69f9ab24.cohuck@redhat.com> <7ad94e6b-7e5e-04f6-109a-990075a1d8c2@linux.ibm.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=207.211.31.120; envelope-from=cohuck@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/24 02:33:25 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=_AUTOLEARN 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: Thomas Huth , frankja@linux.ibm.com, david@redhat.com, mst@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, 24 Jun 2020 10:49:57 -0400 Collin Walling wrote: > On 6/24/20 8:55 AM, Cornelia Huck wrote: > > On Wed, 24 Jun 2020 14:40:58 +0200 > > Thomas Huth wrote: > > > >> On 24/06/2020 14.36, Cornelia Huck wrote: > >>> On Thu, 18 Jun 2020 18:22:56 -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 | 21 ++++++++++++++++++++- > >>>> 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, 31 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c > >>>> index 0dfbe6e5ec..f7c49e339e 100644 > >>>> --- a/hw/s390x/sclp.c > >>>> +++ b/hw/s390x/sclp.c > >>>> @@ -56,6 +56,18 @@ static bool sccb_has_valid_boundary(uint64_t sccb_addr, uint32_t code, > >>>> uint64_t sccb_boundary = (sccb_addr & PAGE_MASK) + PAGE_SIZE; > >>>> > >>>> switch (code & SCLP_CMD_CODE_MASK) { > >>>> + case SCLP_CMDW_READ_SCP_INFO: > >>>> + case SCLP_CMDW_READ_SCP_INFO_FORCED: > >>>> + case SCLP_CMDW_READ_CPU_INFO: > >>>> + /* > >>>> + * An extended-length SCCB is only allowed for Read SCP/CPU Info and > >>>> + * is allowed to exceed the 4k boundary. The respective commands will > >>>> + * set the length field to the required length if an insufficient > >>>> + * SCCB length is provided. > >>>> + */ > >>>> + if (s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB)) { > >>>> + return true; > >>>> + } > >>> > >>> Add a fallthrough annotation? > >> > >> ... otherwise Coverity and friends will complain later. > > > > Nod. > > > > Something simple like... > > /* without this feature, these commands must respect the 4k boundary */ > > ? No, I meant something that is parsed by static checkers (/* fallthrough */ seems to be the common marker for that in QEMU). I think what the fallthrough does is already clear enough to humans. > > >> > >>>> default: > >>>> if (sccb_max_addr < sccb_boundary) { > >>>> return true;