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

From: Pierre Morel
Date: Tue Aug 03 2021 - 04:27:06 EST

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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@xxxxxxxxxxxxx>
---
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;
+
if (test_kvm_facility(vcpu->kvm, 73))
vcpu->arch.sie_block->ecb |= ECB_TE;

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 4002a24bc43a..50d67190bf65 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 d9e4aabcb31a..081ce0cd44b9 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_BINARY_STATS_FD 203
#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
#define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_S390_CPU_TOPOLOGY 206

#ifdef KVM_CAP_IRQ_ROUTING

--
2.25.1

Next message: Pierre Morel: "[PATCH v3 3/3] s390x: optimization of the check for CPU topology change"
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