hw/i386/vmport: Allow x2apic without IR

Signal to guest that hypervisor supports x2apic without VT-d/IOMMU
Interrupt-Remapping support. This allows guest to use x2apic in
case all APIC IDs fits in 8-bit (i.e. Max APIC ID < 255).

See Linux kernel commit 4cca6ea04d31 ("x86/apic: Allow x2apic
without IR on VMware platform") and Linux try_to_enable_x2apic()
function.
Reviewed-by: NNikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: NLiran Alon <liran.alon@oracle.com>
Message-Id: <20200312165431.82118-14-liran.alon@oracle.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/i386/vmport.c

@@ -176,7 +176,14 @@ static uint32_t vmport_cmd_ram_size(void *opaque, uint32_t addr)
 
 static uint32_t vmport_cmd_get_vcpu_info(void *opaque, uint32_t addr)
 {
-    return 1 << VCPU_INFO_RESERVED_BIT;
+    X86CPU *cpu = X86_CPU(current_cpu);
+    uint32_t ret = 0;
+
+    if (cpu->env.features[FEAT_1_ECX] & CPUID_EXT_X2APIC) {
+        ret |= 1 << VCPU_INFO_LEGACY_X2APIC_BIT;
+    }
+
+    return ret;
 }
 
 static const MemoryRegionOps vmport_ops = {