s390: guest support for diagnose 0x318

s390: guest support for diagnose 0x318

DIAGNOSE 0x318 (diag318) is an s390 instruction that allows the storage
of diagnostic information that is collected by the firmware in the case
of hardware/firmware service events.

QEMU handles the instruction by storing the info in the CPU state. A
subsequent register sync will communicate the data to the hypervisor.

QEMU handles the migration via a VM State Description.

This feature depends on the Extended-Length SCCB (els) feature. If
els is not present, then a warning will be printed and the SCLP bit
that allows the Linux kernel to execute the instruction will not be
set.

Availability of this instruction is determined by byte 134 (aka fac134)
bit 0 of the SCLP Read Info block. This coincidentally expands into the
space used for CPU entries, which means VMs running with the diag318
capability may not be able to read information regarding all CPUs
unless the guest kernel supports an extended-length SCCB.

This feature is not supported in protected virtualization mode.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20200915194416.107460-9-walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>