[PATCH v10 3/3] KVM: s390: resetting the Topology-Change-Report

Pierre Morel
2022-06-20T12:50:36Z

During a subsystem reset the Topology-Change-Report is cleared.
Let's give userland the possibility to clear the MTCR in the case
of a subsystem reset.

To migrate the MTCR, we give userland the possibility to
query the MTCR state.

We indicate KVM support for the CPU topology facility with a new
KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
Documentation/virt/kvm/api.rst | 31 +++++++++++
arch/s390/include/uapi/asm/kvm.h | 10 ++++
arch/s390/kvm/kvm-s390.c | 96 ++++++++++++++++++++++++++++++++
include/uapi/linux/kvm.h | 1 +
4 files changed, 138 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 11e00a46c610..326f8b7e7671 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7956,6 +7956,37 @@ should adjust CPUID leaf 0xA to reflect that the PMU is disabled.
When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of
type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request.

+8.37 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.
+
+When this capability is present, KVM provides a new attribute group
+on vm fd, KVM_S390_VM_CPU_TOPOLOGY.
+This new attribute allows to get, set or clear the Modified Change
+Topology Report (MTCR) bit of the SCA through the kvm_device_attr
+structure.
+
+Getting the MTCR bit is realized by using a kvm_device_attr attr
+entry value of KVM_GET_DEVICE_ATTR and with kvm_device_attr addr
+entry pointing to the address of a struct kvm_cpu_topology.
+The value of the MTCR is return by the bit mtcr of the structure.
+
+When using KVM_SET_DEVICE_ATTR the MTCR is set by using the
+attr->attr value KVM_S390_VM_CPU_TOPO_MTCR_SET and cleared by
+using KVM_S390_VM_CPU_TOPO_MTCR_CLEAR.
+
9. Known KVM API problems
=========================

diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index 7a6b14874d65..df5e8279ffd0 100644
--- a/arch/s390/include/uapi/asm/kvm.h
+++ b/arch/s390/include/uapi/asm/kvm.h
@@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
#define KVM_S390_VM_CRYPTO 2
#define KVM_S390_VM_CPU_MODEL 3
#define KVM_S390_VM_MIGRATION 4
+#define KVM_S390_VM_CPU_TOPOLOGY 5

/* kvm attributes for mem_ctrl */
#define KVM_S390_VM_MEM_ENABLE_CMMA 0
@@ -171,6 +172,15 @@ struct kvm_s390_vm_cpu_subfunc {
#define KVM_S390_VM_MIGRATION_START 1
#define KVM_S390_VM_MIGRATION_STATUS 2

+/* kvm attributes for cpu topology */
+#define KVM_S390_VM_CPU_TOPO_MTCR_CLEAR 0
+#define KVM_S390_VM_CPU_TOPO_MTCR_SET 1
+
+struct kvm_cpu_topology {
+ __u16 mtcr : 1;
+ __u16 reserved : 15;
+};
+
/* for KVM_GET_REGS and KVM_SET_REGS */
struct kvm_regs {
/* general purpose regs for s390 */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 95b96019ca8e..ae39041bb149 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;
@@ -1710,6 +1727,76 @@ static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
ipte_unlock(kvm);
}

+/**
+ * kvm_s390_sca_clear_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * Updates the Multiprocessor Topology-Change-Report to signal
+ * the guest with a topology change.
+ */
+static void kvm_s390_sca_clear_mtcr(struct kvm *kvm)
+{
+ struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
+
+ ipte_lock(kvm);
+ sca->utility &= ~SCA_UTILITY_MTCR;
+ ipte_unlock(kvm);
+}
+
+static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+ if (!test_kvm_facility(kvm, 11))
+ return -ENXIO;
+
+ switch (attr->attr) {
+ case KVM_S390_VM_CPU_TOPO_MTCR_SET:
+ kvm_s390_sca_set_mtcr(kvm);
+ break;
+ case KVM_S390_VM_CPU_TOPO_MTCR_CLEAR:
+ kvm_s390_sca_clear_mtcr(kvm);
+ break;
+ }
+ return 0;
+}
+
+/**
+ * kvm_s390_sca_get_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * reports to QEMU the Multiprocessor Topology-Change-Report.
+ */
+static int kvm_s390_sca_get_mtcr(struct kvm *kvm)
+{
+ struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
+ int val;
+
+ ipte_lock(kvm);
+ val = sca->utility & SCA_UTILITY_MTCR;
+ ipte_unlock(kvm);
+
+ return val;
+}
+
+static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+ struct kvm_cpu_topology topo = {};
+
+ if (!test_kvm_facility(kvm, 11))
+ return -ENXIO;
+
+ topo.mtcr = kvm_s390_sca_get_mtcr(kvm) ? 1 : 0;
+ if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo)))
+ return -EFAULT;
+
+ return 0;
+}
+
static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
{
int ret;
@@ -1730,6 +1817,9 @@ static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = kvm_s390_vm_set_migration(kvm, attr);
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = kvm_s390_set_topology(kvm, attr);
+ break;
default:
ret = -ENXIO;
break;
@@ -1755,6 +1845,9 @@ static int kvm_s390_vm_get_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = kvm_s390_vm_get_migration(kvm, attr);
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = kvm_s390_get_topology(kvm, attr);
+ break;
default:
ret = -ENXIO;
break;
@@ -1828,6 +1921,9 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = 0;
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = test_kvm_facility(kvm, 11) ? 0 : -ENXIO;
+ break;
default:
ret = -ENXIO;
break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5088bd9f1922..33317d820032 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1157,6 +1157,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_VM_TSC_CONTROL 214
#define KVM_CAP_SYSTEM_EVENT_DATA 215
#define KVM_CAP_ARM_SYSTEM_SUSPEND 216
+#define KVM_CAP_S390_CPU_TOPOLOGY 217

#ifdef KVM_CAP_IRQ_ROUTING

--
2.31.1