On Thu, 10 Sep 2020 05:36:53 -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 | 43 +++++++++++++++++++++++++---- > include/hw/s390x/sclp.h | 1 + > target/s390x/cpu_features_def.h.inc | 1 + > target/s390x/gen-features.c | 1 + > target/s390x/kvm.c | 8 ++++++ > 5 files changed, 48 insertions(+), 6 deletions(-) Acked-by: Cornelia Huck <coh...@redhat.com>