Re: [PATCH v11 3/3] KVM: s390: resetting the Topology-Change-Report

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On 7/4/22 11:35, Janis Schoetterl-Glausch wrote:
On 7/1/22 18:25, Pierre Morel wrote:
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@xxxxxxxxxxxxx>
---
  Documentation/virt/kvm/api.rst   | 25 +++++++++++++++
  arch/s390/include/uapi/asm/kvm.h | 10 ++++++
  arch/s390/kvm/kvm-s390.c         | 53 ++++++++++++++++++++++++++++++++
  include/uapi/linux/kvm.h         |  1 +
  4 files changed, 89 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 11e00a46c610..5e086125d8ad 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7956,6 +7956,31 @@ 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 latter only if the user STSI capability is also enabled.

Hum, not sure about this.
we can not set facility 11 and return 3 to STSI(15) for valid selectors.

I think that it was right before, KVM_CAP_S390_CPU_TOPOLOGY and KVM_CAP_S390_USER_STSI are independent in KVM, userland can turn on one and not the other.
But KVM proposes both.

Of course it is stupid to turn on only KVM_CAP_S390_CPU_TOPOLOGY but KVM is not responsible for this userland is.

Otherwise, we need to check on KVM_CAP_S390_USER_STSI before authorizing KVM_CAP_S390_CPU_TOPOLOGY and that looks even more complicated for me, or we suppress the KVM_CAP_S390_CPU_TOPOLOGY and implement the all stsi(15) in the kernel what I really do not think is good because of the complexity of the userland API

+
+The stfle facility 11, CPU Topology facility, should not be indicated
+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.
+
+When getting the Modified Change Topology Report value, the attr->addr
+must point to a byte where the value will be stored.
+
  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;
+};

This is no longer used, is it?

No, I sent the wrong patch it seems!! Sorry for that.
There is nothing more in kvm.h now but the definition for KVM_S390_VM_CPU_TOPOLOGY




+
  /* 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 ee59b03f2e45..5029fe40adbd 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",

I still would go for consistency here, "ENABLE: CAP_S390_CPU_TOPOLOGY %s".

Yes, done.


+			 r ? "(not available)" : "(success)");
+		break;
  	default:
  		r = -EINVAL;
  		break;
@@ -1716,6 +1733,33 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)
  	read_unlock(&kvm->arch.sca_lock);
  }
+static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	kvm_s390_update_topology_change_report(kvm, !!attr->attr);

Will this not be automatically clamped to 0,1 if the argument has type bool?

I do not know, anyway done like this is sure.

+	return 0;
+}
+
+static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+	union sca_utility utility;
+	struct bsca_block *sca = kvm->arch.sca;
+	__u8 topo;
+
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
         read_lock(&kvm->arch.sca_lock);
         utility.val = READ_ONCE(kvm->arch.sca->utility.val);
         read_unlock(&kvm->arch.sca_lock); >
And then get rid of the sca declaration.


OK

+	topo = utility.mtcr;
+
+	if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo)))
+		return -EFAULT;
+
+	return 0;
+}
+
[...]


--
Pierre Morel
IBM Lab Boeblingen



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