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Wed, 24 Jun 2020 12:41:00 +0000 (UTC) Subject: Re: [PATCH v3 6/8] s390/sclp: add extended-length sccb support for kvm guest To: Cornelia Huck , Collin Walling References: <20200618222258.23287-1-walling@linux.ibm.com> <20200618222258.23287-7-walling@linux.ibm.com> <20200624143635.2d87c1ca.cohuck@redhat.com> From: Thomas Huth Message-ID: Date: Wed, 24 Jun 2020 14:40:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200624143635.2d87c1ca.cohuck@redhat.com> Content-Language: en-US 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=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=thuth@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: 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 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. >> default: >> if (sccb_max_addr < sccb_boundary) { >> return true; >> @@ -72,6 +84,10 @@ static bool sccb_sufficient_len(SCCB *sccb, int num_cpus, int data_len) >> >> if (be16_to_cpu(sccb->h.length) < required_len) { >> sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH); >> + if (s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB) && >> + sccb->h.control_mask[2] & SCLP_VARIABLE_LENGTH_RESPONSE) { >> + sccb->h.length = required_len; >> + } >> return false; >> } >> return true; >> @@ -101,7 +117,9 @@ static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count) >> */ >> static inline int get_read_scp_info_data_len(void) >> { >> - return offsetof(ReadInfo, entries); >> + return s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB) ? >> + offsetof(ReadInfo, entries) : >> + SCLP_READ_SCP_INFO_FIXED_CPU_OFFSET; >> } >> >> /* Provide information about the configuration, CPUs and storage */ >> @@ -116,6 +134,7 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb) >> CPUEntry *entries_start = (void *)sccb + data_len; >> >> if (!sccb_sufficient_len(sccb, machine->possible_cpus->len, data_len)) { >> + warn_report("insufficient sccb size to store read scp info response"); > > Hm, this warning is triggered by a guest action, isn't it? Not sure how > helpful it is. I think this should be qemu_log_mask(LOG_GUEST_ERROR, ...) instead? Thomas