target/i386: Set maximum APIC ID to KVM prior to vCPU creation

Specify maximum possible APIC ID assigned for current VM session to KVM
prior to the creation of vCPUs. By this setting, KVM can set up VM-scoped
data structure indexed by the APIC ID, e.g. Posted-Interrupt Descriptor
pointer table to support Intel IPI virtualization, with the most optimal
memory footprint.

It can be achieved by calling KVM_ENABLE_CAP for KVM_CAP_MAX_VCPU_ID
capability once KVM has enabled it. Ignoring the return error if KVM
doesn't support this capability yet.

Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220825025246.26618-1-guang.zeng@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/x86.c

@@ -140,6 +140,10 @@ void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version)
         exit(EXIT_FAILURE);
     }
 
+    if (kvm_enabled()) {
+        kvm_set_max_apic_id(x86ms->apic_id_limit);
+    }
+
     possible_cpus = mc->possible_cpu_arch_ids(ms);
     for (i = 0; i < ms->smp.cpus; i++) {
         x86_cpu_new(x86ms, possible_cpus->cpus[i].arch_id, &error_fatal);

target/i386/kvm/kvm-stub.c

@@ -44,3 +44,8 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
 {
     abort();
 }
+
+void kvm_set_max_apic_id(uint32_t max_apic_id)
+{
+    return;
+}

target/i386/kvm/kvm.c

@@ -5723,3 +5723,8 @@ void kvm_arch_accel_class_init(ObjectClass *oc)
                                           "Clock cycles without an event window "
                                           "after which a notification VM exit occurs");
 }
+
+void kvm_set_max_apic_id(uint32_t max_apic_id)
+{
+    kvm_vm_enable_cap(kvm_state, KVM_CAP_MAX_VCPU_ID, 0, max_apic_id);
+}

target/i386/kvm/kvm_i386.h

@@ -66,4 +66,6 @@ typedef struct kvm_msr_handlers {
 bool kvm_filter_msr(KVMState *s, uint32_t msr, QEMURDMSRHandler *rdmsr,
                     QEMUWRMSRHandler *wrmsr);
 
+void kvm_set_max_apic_id(uint32_t max_apic_id);
+
 #endif