s390/sclp: add extended-length sccb support for kvm guest

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 <walling@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20200915194416.107460-7-walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

3 files changed, 10 insertions, 0 deletions

diff --git a/target/s390x/cpu_features_def.h.inc b/target/s390x/cpu_features_def.h.inc
index 5942f81..1c04cc1 100644
--- a/target/s390x/cpu_features_def.h.inc
+++ b/target/s390x/cpu_features_def.h.inc
@@ -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 8ddeebc..6857f65 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 f2f75d2..a2d5ad7 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -2456,6 +2456,14 @@ 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.
+     * For PV guests this is completely fenced by the Ultravisor, as Service
+     * Call error checking and STFLE interpretation are handled via SIE.
+     */
+    set_bit(S390_FEAT_EXTENDED_LENGTH_SCCB, model->features);
+
     /* strip of features that are not part of the maximum model */
     bitmap_and(model->features, model->features, model->def->full_feat,
                S390_FEAT_MAX);