On 5/18/20 4:55 AM, Janosch Frank wrote:
> On 5/16/20 12:20 AM, 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 <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 | 4 ++++
>> 5 files changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index 755f5f3fab..bde4c5420e 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 allowed_len = (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 RSCPI and RSCPU 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;
>> + }
>> default:
>> if (current_len <= allowed_len) {
>> return true;
>> @@ -72,6 +84,10 @@ static bool sccb_has_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 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_has_sufficient_len(sccb, machine->possible_cpus->len,
>> data_len)) {
>> + warn_report("insufficient sccb size to store full read scp info
>> response");
>> return;
>> }
>>
>> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
>> index 822eff4396..ef2d63eae9 100644
>> --- a/include/hw/s390x/sclp.h
>> +++ b/include/hw/s390x/sclp.h
>> @@ -110,6 +110,7 @@ typedef struct CPUEntry {
>> uint8_t reserved1;
>> } QEMU_PACKED CPUEntry;
>>
>> +#define SCLP_READ_SCP_INFO_FIXED_CPU_OFFSET 128
>> typedef struct ReadInfo {
>> SCCBHeader h;
>> uint16_t rnmax;
>> diff --git a/target/s390x/cpu_features_def.inc.h
>> b/target/s390x/cpu_features_def.inc.h
>> index 60db28351d..3548d65a69 100644
>> --- a/target/s390x/cpu_features_def.inc.h
>> +++ b/target/s390x/cpu_features_def.inc.h
>> @@ -97,6 +97,7 @@ DEF_FEAT(GUARDED_STORAGE, "gs", STFL, 133,
>> "Guarded-storage facility")
>> DEF_FEAT(VECTOR_PACKED_DECIMAL, "vxpd", STFL, 134, "Vector packed decimal
>> facility")
>> DEF_FEAT(VECTOR_ENH, "vxeh", STFL, 135, "Vector enhancements facility")
>> DEF_FEAT(MULTIPLE_EPOCH, "mepoch", STFL, 139, "Multiple-epoch facility")
>> +DEF_FEAT(EXTENDED_LENGTH_SCCB, "els", STFL, 140, "Extended-length SCCB
>> facility")
>> DEF_FEAT(TEST_PENDING_EXT_INTERRUPTION, "tpei", STFL, 144,
>> "Test-pending-external-interruption facility")
>> DEF_FEAT(INSERT_REFERENCE_BITS_MULT, "irbm", STFL, 145,
>> "Insert-reference-bits-multiple facility")
>> DEF_FEAT(MSA_EXT_8, "msa8-base", STFL, 146,
>> "Message-security-assist-extension-8 facility (excluding subfunctions)")
>> diff --git a/target/s390x/gen-features.c b/target/s390x/gen-features.c
>> index 8ddeebc544..6857f657fb 100644
>> --- a/target/s390x/gen-features.c
>> +++ b/target/s390x/gen-features.c
>> @@ -522,6 +522,7 @@ static uint16_t full_GEN12_GA1[] = {
>> S390_FEAT_AP_QUEUE_INTERRUPT_CONTROL,
>> S390_FEAT_AP_FACILITIES_TEST,
>> S390_FEAT_AP,
>> + S390_FEAT_EXTENDED_LENGTH_SCCB,
>> };
>>
>> static uint16_t full_GEN12_GA2[] = {
>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>> index 69881a0da0..380fb81822 100644
>> --- a/target/s390x/kvm.c
>> +++ b/target/s390x/kvm.c
>> @@ -2456,6 +2456,10 @@ void kvm_s390_get_host_cpu_model(S390CPUModel *model,
>> Error **errp)
>> KVM_S390_VM_CRYPTO_ENABLE_APIE)) {
>> set_bit(S390_FEAT_AP, model->features);
>> }
>> +
>> + /* Extended-Length SCCB is handled entirely within QEMU */
>> + set_bit(S390_FEAT_EXTENDED_LENGTH_SCCB, model->features);
>> +
>
> We need to fence this for secure guests as the SIDA is only 4k at the
> moment.
>
I don't know much about the SE stuff, so I'll take your word for it.
Should this follow the same fencing as diag 318 and simply check for pv
mode?
> Do we need to take extra steps for migration safety?
> I guess this is only available with host-passthrough or -model?
>
>> /* strip of features that are not part of the maximum model */
>> bitmap_and(model->features, model->features, model->def->full_feat,
>> S390_FEAT_MAX);
>>
>
>
--
--
Regards,
Collin
Stay safe and stay healthy
