On Thu, 18 Jun 2020 18:22:56 -0400 Collin Walling <wall...@linux.ibm.com> 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 <wall...@linux.ibm.com> > --- > 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? > 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. > return; > } > (...) Otherwise, looks good to me.