On 6/24/20 8:55 AM, Cornelia Huck wrote: > On Wed, 24 Jun 2020 14:40:58 +0200 > Thomas Huth <th...@redhat.com> wrote: > >> On 24/06/2020 14.36, Cornelia Huck wrote: >>> 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? >> >> ... otherwise Coverity and friends will complain later. > > Nod. >
Something simple like... /* without this feature, these commands must respect the 4k boundary */ ? >> >>>> 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? > > Yes, that sounds better. > > Sure, sounds good. -- Regards, Collin Stay safe and stay healthy