On Thu, 2022-02-17 at 10:59 +0100, Pierre Morel wrote:
[...]
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c[...]
index 2296b1ff1e02..af7ea8488fa2 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
-void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+/**
+ * kvm_s390_vcpu_set_mtcr
+ * @vcp: the virtual CPU
+ *
+ * Is only relevant if the topology facility is present.
+ *
+ * Updates the Multiprocessor Topology-Change-Report to signal
+ * the guest with a topology change.
+ */
+static void kvm_s390_vcpu_set_mtcr(struct kvm_vcpu *vcpu)
{
+ struct esca_block *esca = vcpu->kvm->arch.sca;
utility is at the same offset for the bsca and the esca, still
wondering whether it is a good idea to assume esca here...
[...]
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 098831e815e6..af04ffbfd587 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -503,4 +503,29 @@ void kvm_s390_vcpu_crypto_reset_all(struct kvm
*kvm);
*/
extern unsigned int diag9c_forwarding_hz;
+#define S390_KVM_TOPOLOGY_NEW_CPU -1
+/**
+ * kvm_s390_topology_changed
+ * @vcpu: the virtual CPU
+ *
+ * If the topology facility is present, checks if the CPU toplogy
+ * viewed by the guest changed due to load balancing or CPU hotplug.
+ */
+static inline bool kvm_s390_topology_changed(struct kvm_vcpu *vcpu)
+{
+ if (!test_kvm_facility(vcpu->kvm, 11))
+ return false;
+
+ /* A new vCPU has been hotplugged */
+ if (vcpu->arch.prev_cpu == S390_KVM_TOPOLOGY_NEW_CPU)
+ return true;
+
+ /* The real CPU backing up the vCPU moved to another socket
*/
+ if (topology_physical_package_id(vcpu->cpu) !=
+ topology_physical_package_id(vcpu->arch.prev_cpu))
+ return true;
Why is it OK to look just at the physical package ID here? What if the
vcpu for example moves to a different book, which has a core with the
same physical package ID?