Re: [PATCH v9 3/3] s390x: KVM: resetting the Topology-Change-Report

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On 5/12/22 11:31, David Hildenbrand wrote:
On 06.05.22 11:24, 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, let's give userland the possibility to
query the MTCR state.

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
  arch/s390/include/uapi/asm/kvm.h |  5 ++
  arch/s390/kvm/kvm-s390.c         | 79 ++++++++++++++++++++++++++++++++
  2 files changed, 84 insertions(+)

diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index 7a6b14874d65..abdcf4069343 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 +172,10 @@ 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_MTR_CLEAR	0
+#define KVM_S390_VM_CPU_TOPO_MTR_SET	1
+
  /* 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 c8bdce31464f..80a1244f0ead 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1731,6 +1731,76 @@ 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;


One space too much.

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_MTR_SET:
+		kvm_s390_sca_set_mtcr(kvm);
+		break;
+	case KVM_S390_VM_CPU_TOPO_MTR_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)
+{
+	int mtcr;

I think we prefer something like u16 when copying to user space.

If you prefer.
The original idea was to have something like a bool but then I should have change get_mtcr to has_mtcr.



+
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	mtcr = kvm_s390_sca_get_mtcr(kvm);
+	if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr)))
+		return -EFAULT;
+
+	return 0;
+}

You should probably add documentation, and document that only the last
bit (0x1) has a meaning.

Apart from that LGTM.


--
Pierre Morel
IBM Lab Boeblingen



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