Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report

David Hildenbrand
2021-08-31T14:03:53Z

On 03.08.21 10:26, Pierre Morel wrote:
> We let the userland hypervisor know if the machine support the CPU
> topology facility using a new KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.
>
> The PTF instruction will report a topology change if there is any change
> with a previous STSI_15_2 SYSIB.
> Changes inside a STSI_15_2 SYSIB occur if CPU bits are set or clear
> inside the CPU Topology List Entry CPU mask field, which happens with
> changes in CPU polarization, dedication, CPU types and adding or
> removing CPUs in a socket.
>
> The reporting to the guest is done using the Multiprocessor
> Topology-Change-Report (MTCR) bit of the utility entry of the guest's
> SCA which will be cleared during the interpretation of PTF.
>
> To check if the topology has been modified we use a new field of the
> arch vCPU to save the previous real CPU ID at the end of a schedule
> and verify on next schedule that the CPU used is in the same socket.
>
> We deliberatly ignore:
> - polarization: only horizontal polarization is currently used in linux.
> - CPU Type: only IFL Type are supported in Linux
> - Dedication: we consider that only a complete dedicated CPU stack can
> take benefit of the CPU Topology.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> arch/s390/include/asm/kvm_host.h | 14 +++++++---
> arch/s390/kvm/kvm-s390.c | 48 +++++++++++++++++++++++++++++++-
> arch/s390/kvm/vsie.c | 3 ++
> include/uapi/linux/kvm.h | 1 +
> 4 files changed, 61 insertions(+), 5 deletions(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 9b4473f76e56..b7effdc96a7a 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -95,15 +95,19 @@ struct bsca_block {
> union ipte_control ipte_control;
> __u64 reserved[5];
> __u64 mcn;
> - __u64 reserved2;
> +#define ESCA_UTILITY_MTCR 0x8000
> + __u16 utility;
> + __u8 reserved2[6];
> struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
> };
>
> struct esca_block {
> union ipte_control ipte_control;
> - __u64 reserved1[7];
> + __u64 reserved1[6];
> + __u16 utility;
> + __u8 reserved2[6];
> __u64 mcn[4];
> - __u64 reserved2[20];
> + __u64 reserved3[20];
> struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];
> };
>
> @@ -228,7 +232,7 @@ struct kvm_s390_sie_block {
> __u8 icptcode; /* 0x0050 */
> __u8 icptstatus; /* 0x0051 */
> __u16 ihcpu; /* 0x0052 */
> - __u8 reserved54; /* 0x0054 */
> + __u8 mtcr; /* 0x0054 */
> #define IICTL_CODE_NONE 0x00
> #define IICTL_CODE_MCHK 0x01
> #define IICTL_CODE_EXT 0x02
> @@ -246,6 +250,7 @@ struct kvm_s390_sie_block {
> #define ECB_TE 0x10
> #define ECB_SRSI 0x04
> #define ECB_HOSTPROTINT 0x02
> +#define ECB_PTF 0x01
> __u8 ecb; /* 0x0061 */
> #define ECB2_CMMA 0x80
> #define ECB2_IEP 0x20
> @@ -747,6 +752,7 @@ struct kvm_vcpu_arch {
> bool skey_enabled;
> struct kvm_s390_pv_vcpu pv;
> union diag318_info diag318_info;
> + int prev_cpu;
> };
>
> struct kvm_vm_stat {
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index b655a7d82bf0..ff6d8a2b511c 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -568,6 +568,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_S390_VCPU_RESETS:
> case KVM_CAP_SET_GUEST_DEBUG:
> case KVM_CAP_S390_DIAG318:
> + case KVM_CAP_S390_CPU_TOPOLOGY:
> r = 1;
> break;
> case KVM_CAP_SET_GUEST_DEBUG2:
> @@ -819,6 +820,23 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
> icpt_operexc_on_all_vcpus(kvm);
> r = 0;
> break;
> + case KVM_CAP_S390_CPU_TOPOLOGY:
> + mutex_lock(&kvm->lock);
> + if (kvm->created_vcpus) {
> + r = -EBUSY;
> + } else {
> + set_kvm_facility(kvm->arch.model.fac_mask, 11);
> + set_kvm_facility(kvm->arch.model.fac_list, 11);
> + r = 0;
> + }
> + mutex_unlock(&kvm->lock);
> + VM_EVENT(kvm, 3, "ENABLE: CPU TOPOLOGY %s",
> + r ? "(not available)" : "(success)");
> + break;
> +
> + r = -EINVAL;
> + break;
> +
> default:
> r = -EINVAL;
> break;
> @@ -3067,18 +3085,41 @@ __u64 kvm_s390_get_cpu_timer(struct kvm_vcpu *vcpu)
> return value;
> }
>
> -void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> +static void kvm_s390_set_mtcr(struct kvm_vcpu *vcpu)
> {
> + struct esca_block *esca = vcpu->kvm->arch.sca;
> +
> + if (vcpu->arch.sie_block->ecb & ECB_PTF) {
> + ipte_lock(vcpu);
> + WRITE_ONCE(esca->utility, ESCA_UTILITY_MTCR);
> + ipte_unlock(vcpu);
> + }
> +}
>
> +void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> +{
> gmap_enable(vcpu->arch.enabled_gmap);
> kvm_s390_set_cpuflags(vcpu, CPUSTAT_RUNNING);
> if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu))
> __start_cpu_timer_accounting(vcpu);
> vcpu->cpu = cpu;
> +
> + /*
> + * With PTF interpretation the guest will be aware of topology
> + * change by the Multiprocessor Topology-Change-Report is pending.
> + * Check for reasons to make the MTCR pending and make it pending.
> + */
> + if ((vcpu->arch.sie_block->ecb & ECB_PTF) &&
> + cpu != vcpu->arch.prev_cpu) {
> + if (cpu_topology[cpu].socket_id !=
> + cpu_topology[vcpu->arch.prev_cpu].socket_id)
> + kvm_s390_set_mtcr(vcpu);
> + }
> }
>
> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> {
> + vcpu->arch.prev_cpu = vcpu->cpu;
> vcpu->cpu = -1;
> if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu))
> __stop_cpu_timer_accounting(vcpu);
> @@ -3198,6 +3239,11 @@ static int kvm_s390_vcpu_setup(struct kvm_vcpu *vcpu)
> vcpu->arch.sie_block->ecb |= ECB_HOSTPROTINT;
> if (test_kvm_facility(vcpu->kvm, 9))
> vcpu->arch.sie_block->ecb |= ECB_SRSI;
> +
> + /* PTF needs both host and guest facilities to enable interpretation */
> + if (test_kvm_facility(vcpu->kvm, 11) && test_facility(11))
> + vcpu->arch.sie_block->ecb |= ECB_PTF;

Again, doesn't test_kvm_facility(vcpu->kvm, 11) imply that we have host
support by checking fac_mask?

--
Thanks,

David / dhildenb