On Wed, 24 Jun 2020 16:23:10 -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 | 24 +++++++++++++++++++++++-
> 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, 34 insertions(+), 1 deletion(-)
>
(...)
> @@ -111,6 +131,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
> CPUEntry *entries_start = (void *)sccb + offset_cpu;
>
> if (!sccb_verify_length(sccb, machine->possible_cpus->len, offset_cpu)) {
> + qemu_log_mask(LOG_GUEST_ERROR, "insufficient sccb size to store "
> + "read scp info response\n");
Not sure if logging needed/provided length would be helpful here.
> return;
> }
>
(...)
Acked-by: Cornelia Huck <coh...@redhat.com>
