[PULL 3/5] target/i386: Set maximum APIC ID to KVM prior to vCPU creation

[Paolo Bonzini]

From: Zeng Guang <guang.zeng@intel.com>

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              | 4 ++++
 target/i386/kvm/kvm-stub.c | 5 +++++
 target/i386/kvm/kvm.c      | 5 +++++
 target/i386/kvm/kvm_i386.h | 2 ++
 4 files changed, 16 insertions(+)

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index bd50a064a36d..78cc131926c8 100644
--- a/hw/i386/x86.c
+++ b/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);
diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
index f6e7e4466e1a..e052f1c7b0ef 100644
--- a/target/i386/kvm/kvm-stub.c
+++ b/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;
+}
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 4df04280890a..a21320937943 100644
--- a/target/i386/kvm/kvm.c
+++ b/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);
+}
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index b7c38ba2c462..6a5c24e3dc40 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/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
-- 
2.38.1