hw/i386/pc: enable PVH only for machine type >= 4.0

In order to avoid migration issues, we enable PVH only for
machine type >= 4.0
Suggested-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/i386/pc.c

@@ -1220,7 +1220,8 @@ static void load_linux(PCMachineState *pcms,
          * saving the PVH entry point used by the x86/HVM direct boot ABI.
          * If load_elfboot() is successful, populate the fw_cfg info.
          */
-        if (load_elfboot(kernel_filename, kernel_size,
+        if (pcmc->pvh_enabled &&
+            load_elfboot(kernel_filename, kernel_size,
                          header, pvh_start_addr, fw_cfg)) {
             fclose(f);
 
@@ -2783,6 +2784,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     pcmc->acpi_data_size = 0x20000 + 0x8000;
     pcmc->save_tsc_khz = true;
     pcmc->linuxboot_dma_enabled = true;
+    pcmc->pvh_enabled = true;
     assert(!mc->get_hotplug_handler);
     mc->get_hotplug_handler = pc_get_hotplug_handler;
     mc->cpu_index_to_instance_props = pc_cpu_index_to_props;

hw/i386/pc_piix.c

@@ -440,9 +440,12 @@ DEFINE_I440FX_MACHINE(v4_0, "pc-i440fx-4.0", NULL,
 
 static void pc_i440fx_3_1_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+
     pc_i440fx_4_0_machine_options(m);
     m->is_default = 0;
     m->alias = NULL;
+    pcmc->pvh_enabled = false;
     compat_props_add(m->compat_props, hw_compat_3_1, hw_compat_3_1_len);
     compat_props_add(m->compat_props, pc_compat_3_1, pc_compat_3_1_len);
 }

hw/i386/pc_q35.c

@@ -376,9 +376,12 @@ DEFINE_Q35_MACHINE(v4_0, "pc-q35-4.0", NULL,
 
 static void pc_q35_3_1_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+
     pc_q35_4_0_machine_options(m);
     m->default_kernel_irqchip_split = false;
     m->alias = NULL;
+    pcmc->pvh_enabled = false;
     compat_props_add(m->compat_props, hw_compat_3_1, hw_compat_3_1_len);
     compat_props_add(m->compat_props, pc_compat_3_1, pc_compat_3_1_len);
 }

include/hw/i386/pc.h

@@ -133,6 +133,9 @@ typedef struct PCMachineClass {
 
     /* use DMA capable linuxboot option rom */
     bool linuxboot_dma_enabled;
+
+    /* use PVH to load kernels that support this feature */
+    bool pvh_enabled;
 } PCMachineClass;
 
 #define TYPE_PC_MACHINE "generic-pc-machine"