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. --- I found a slight problem when testing this to run without sca entries. Fixed now and tests are successful with and without using the sca entries (incl. vsie). Changes in v3: - do not enable sigp for guests when kvm_s390_use_sca_entries() is false - consistently use kvm_s390_use_sca_entries() instead of sclp.has_sigpif - Link to v2: https://lore.kernel.org/r/20250519-rm-bsca-v2-0-e3ea53dd0394@xxxxxxxxxxxxx Changes in v2: - properly apply checkpatch --strict (Thanks Claudio) - some small comment wording changes - rebased - Link to v1: https://lore.kernel.org/r/20250514-rm-bsca-v1-0-6c2b065a8680@xxxxxxxxxxxxx --- 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 | 71 ++++---------- arch/s390/kvm/kvm-s390.c | 163 ++++++--------------------------- arch/s390/kvm/kvm-s390.h | 9 +- 6 files changed, 55 insertions(+), 207 deletions(-) --- base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21 change-id: 20250513-rm-bsca-ab1e8649aca7 Best regards, -- Christoph Schlameuss <schlameuss@xxxxxxxxxxxxx>
