On Mon, 18 May 2020 10:55:24 +0200 Janosch Frank <fran...@linux.ibm.com> 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 Nit: I had to stare at this for a bit before I figured out what the acronyms refer to. > > + * 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; (...) > > 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. > > Do we need to take extra steps for migration safety? > I guess this is only available with host-passthrough or -model? What do you mean with '-model'? I think it can be added manually everywhere? But I'm always a bit confused by cpu models. > > > /* strip of features that are not part of the maximum model */ > > bitmap_and(model->features, model->features, model->def->full_feat, > > S390_FEAT_MAX); > > > >
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