Re: [PATCH v5 1/1] s390x: KVM: accept STSI for CPU topology information

Pierre Morel
2021-12-09T13:30:57Z

On 12/9/21 13:36, Claudio Imbrenda wrote:
> On Mon, 22 Nov 2021 14:14:43 +0100
> Pierre Morel <pmorel@linux.ibm.com> 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_1_2 SYSIB.
>> Changes inside a STSI_15_1_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 assume in this patch:
>> - no polarization change: only horizontal polarization is currently
>> used in linux.
>> - no CPU Type change: only IFL Type are supported in Linux
>> - Dedication: with this patch, only a complete dedicated CPU stack can
>> take benefit of the CPU Topology.
>>
>> STSI(15.1.x) gives information on the CPU configuration topology.
>> Let's accept the interception of STSI with the function code 15 and
>> let the userland part of the hypervisor handle it when userland
>> support the CPU Topology facility.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>
> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>
> Although the title of the patch is not very correct, you are doing more
> than just accepting STSI.
>
> Maybe call it "guest PTF support", or "guest support for topology
> function"?

Right, thanks will do.

Thanks for the review.
Pierre

>
>> ---
>> Documentation/virt/kvm/api.rst | 16 ++++++++++
>> arch/s390/include/asm/kvm_host.h | 14 ++++++---
>> arch/s390/kvm/kvm-s390.c | 52 +++++++++++++++++++++++++++++++-
>> arch/s390/kvm/priv.c | 7 ++++-
>> arch/s390/kvm/vsie.c | 3 ++
>> include/uapi/linux/kvm.h | 1 +
>> 6 files changed, 87 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>> index aeeb071c7688..e5c9da0782a6 100644
>> --- a/Documentation/virt/kvm/api.rst
>> +++ b/Documentation/virt/kvm/api.rst
>> @@ -7484,3 +7484,19 @@ The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset
>> of the result of KVM_CHECK_EXTENSION. KVM will forward to userspace
>> the hypercalls whose corresponding bit is in the argument, and return
>> ENOSYS for the others.
>> +
>> +8.17 KVM_CAP_S390_CPU_TOPOLOGY
>> +------------------------------
>> +
>> +:Capability: KVM_CAP_S390_CPU_TOPOLOGY
>> +:Architectures: s390
>> +:Type: vm
>> +
>> +This capability indicates that kvm will provide the S390 CPU Topology facility
>> +which consist of the interpretation of the PTF instruction for the Function
>> +Code 2 along with interception and forwarding of both the PTF instruction
>> +with function Codes 0 or 1 and the STSI(15,1,x) instruction to the userland
>> +hypervisor.
>> +
>> +The stfle facility 11, CPU Topology facility, should not be provided to the
>> +guest without this capability.
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index a604d51acfc8..cccc09a8fdab 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
>> @@ -247,6 +251,7 @@ struct kvm_s390_sie_block {
>> #define ECB_SPECI 0x08
>> #define ECB_SRSI 0x04
>> #define ECB_HOSTPROTINT 0x02
>> +#define ECB_PTF 0x01
>> __u8 ecb; /* 0x0061 */
>> #define ECB2_CMMA 0x80
>> #define ECB2_IEP 0x20
>> @@ -748,6 +753,7 @@ 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 14a18ba5ff2c..b40d2a20bce0 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -606,6 +606,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> case KVM_CAP_S390_PROTECTED:
>> r = is_prot_virt_host();
>> break;
>> + case KVM_CAP_S390_CPU_TOPOLOGY:
>> + r = test_facility(11);
>> + break;
>> default:
>> r = 0;
>> }
>> @@ -817,6 +820,20 @@ 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:
>> + r = -EINVAL;
>> + mutex_lock(&kvm->lock);
>> + if (kvm->created_vcpus) {
>> + r = -EBUSY;
>> + } else if (test_facility(11)) {
>> + 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;
>> default:
>> r = -EINVAL;
>> break;
>> @@ -3089,18 +3106,44 @@ __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 when the Multiprocessor Topology-Change-Report is pending.
>> + * We check for events modifying the result of STSI_15_2:
>> + * - A new vCPU has been hotplugged (prev_cpu == -1)
>> + * - The real CPU backing up the vCPU moved to another socket
>> + */
>> + if (vcpu->arch.sie_block->ecb & ECB_PTF) {
>> + if (vcpu->arch.prev_cpu == -1 ||
>> + (topology_physical_package_id(cpu) !=
>> + topology_physical_package_id(vcpu->arch.prev_cpu)))
>> + kvm_s390_set_mtcr(vcpu);
>> + }
>> }
>>
>> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>> {
>> + /* Remember which CPU was backing the vCPU */
>> + vcpu->arch.prev_cpu = vcpu->cpu;
>> vcpu->cpu = -1;
>> if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu))
>> __stop_cpu_timer_accounting(vcpu);
>> @@ -3220,6 +3263,13 @@ 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 guest facilities to enable interpretation */
>> + if (test_kvm_facility(vcpu->kvm, 11))
>> + vcpu->arch.sie_block->ecb |= ECB_PTF;
>> + /* Set the prev_cpu value to an impossible value to detect a new vcpu */
>> + vcpu->arch.prev_cpu = -1;
>> +
>> if (test_kvm_facility(vcpu->kvm, 73))
>> vcpu->arch.sie_block->ecb |= ECB_TE;
>> if (!kvm_is_ucontrol(vcpu->kvm))
>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>> index 417154b314a6..26d165733496 100644
>> --- a/arch/s390/kvm/priv.c
>> +++ b/arch/s390/kvm/priv.c
>> @@ -861,7 +861,8 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>> if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>> return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>>
>> - if (fc > 3) {
>> + if ((fc > 3 && fc != 15) ||
>> + (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))) {
>> kvm_s390_set_psw_cc(vcpu, 3);
>> return 0;
>> }
>> @@ -898,6 +899,10 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>> goto out_no_data;
>> handle_stsi_3_2_2(vcpu, (void *) mem);
>> break;
>> + case 15:
>> + trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
>> + insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2);
>> + return -EREMOTE;
>> }
>> if (kvm_s390_pv_cpu_is_protected(vcpu)) {
>> memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem,
>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>> index acda4b6fc851..da0397cf2cc7 100644
>> --- a/arch/s390/kvm/vsie.c
>> +++ b/arch/s390/kvm/vsie.c
>> @@ -503,6 +503,9 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>> /* Host-protection-interruption introduced with ESOP */
>> if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_ESOP))
>> scb_s->ecb |= scb_o->ecb & ECB_HOSTPROTINT;
>> + /* CPU Topology */
>> + if (test_kvm_facility(vcpu->kvm, 11))
>> + scb_s->ecb |= scb_o->ecb & ECB_PTF;
>> /* transactional execution */
>> if (test_kvm_facility(vcpu->kvm, 73) && wants_tx) {
>> /* remap the prefix is tx is toggled on */
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 1daa45268de2..273c62dfbe9a 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
>> #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>> #define KVM_CAP_ARM_MTE 205
>> #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
>> +#define KVM_CAP_S390_CPU_TOPOLOGY 207
>>
>> #ifdef KVM_CAP_IRQ_ROUTING
>>