[PATCH v2 0/3] KVM: s390: Use ESCA instead of BSCA at VM init

[Christoph Schlameuss <schlameuss@linux.ibm.com>]

All modern IBM Z and Linux One machines do offer support for the
Extended System Control Area (ESCA). The ESCA is available since the
z114/z196 released in 2010.
KVM needs to allocate and manage the SCA for guest VMs. Prior to this
change the SCA was setup as Basic SCA only supporting a maximum of 64
vCPUs when initializing the VM. With addition of the 65th vCPU the SCA
was needed to be converted to a ESCA.

Instead we will now allocate the ESCA directly upon VM creation
simplifying the code in multiple places as well as completely removing
the need to convert an existing SCA.

In cases where the ESCA is not supported (z10 and earlier) the use of
the SCA entries and with that SIGP interpretation are disabled for VMs.
This increases the number of exits from the VM in multiprocessor
scenarios and thus decreases performance.
The same is true for VSIE where SIGP is currently disabled and thus no
SCA entries are used.

--

v2:
- properly apply checkpatch --strict (Thanks Claudio)
- some small comment wording changes
- rebased

---
Christoph Schlameuss (3):
      KVM: s390: Set KVM_MAX_VCPUS to 256
      KVM: s390: Always allocate esca_block
      KVM: s390: Specify kvm->arch.sca as esca_block

 arch/s390/include/asm/kvm_host.h       |   7 +-
 arch/s390/include/asm/kvm_host_types.h |   2 +
 arch/s390/kvm/gaccess.c                |  10 +-
 arch/s390/kvm/interrupt.c              |  67 ++++----------
 arch/s390/kvm/kvm-s390.c               | 161 ++++++---------------------------
 arch/s390/kvm/kvm-s390.h               |   9 +-
 6 files changed, 52 insertions(+), 204 deletions(-)
---
base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
change-id: 20250513-rm-bsca-ab1e8649aca7

Best regards,
-- 
Christoph Schlameuss <schlameuss@linux.ibm.com>