target/i386: Implement mc->kvm_type() to get VM type

KVM is introducing a new API to create confidential guests, which
will be used by TDX and SEV-SNP but is also available for SEV and
SEV-ES.  The API uses the VM type argument to KVM_CREATE_VM to
identify which confidential computing technology to use.

Since there are no other expected uses of VM types, delegate
mc->kvm_type() for x86 boards to the confidential-guest-support
object pointed to by ms->cgs.

For example, if a sev-guest object is specified to confidential-guest-support,
like,

  qemu -machine ...,confidential-guest-support=sev0 \
       -object sev-guest,id=sev0,...

it will check if a VM type KVM_X86_SEV_VM or KVM_X86_SEV_ES_VM
is supported, and if so use them together with the KVM_SEV_INIT2
function of the KVM_MEMORY_ENCRYPT_OP ioctl. If not, it will fall back to
KVM_SEV_INIT and KVM_SEV_ES_INIT.

This is a preparatory work towards TDX and SEV-SNP support, but it
will also enable support for VMSA features such as DebugSwap, which
are only available via KVM_SEV_INIT2.

Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/x86.c

@@ -1381,6 +1381,16 @@ static void machine_set_sgx_epc(Object *obj, Visitor *v, const char *name,
     qapi_free_SgxEPCList(list);
 }
 
+static int x86_kvm_type(MachineState *ms, const char *vm_type)
+{
+    /*
+     * No x86 machine has a kvm-type property.  If one is added that has
+     * it, it should call kvm_get_vm_type() directly or not use it at all.
+     */
+    assert(vm_type == NULL);
+    return kvm_enabled() ? kvm_get_vm_type(ms) : 0;
+}
+
 static void x86_machine_initfn(Object *obj)
 {
     X86MachineState *x86ms = X86_MACHINE(obj);
@@ -1405,6 +1415,7 @@ static void x86_machine_class_init(ObjectClass *oc, void *data)
     mc->cpu_index_to_instance_props = x86_cpu_index_to_props;
     mc->get_default_cpu_node_id = x86_get_default_cpu_node_id;
     mc->possible_cpu_arch_ids = x86_possible_cpu_arch_ids;
+    mc->kvm_type = x86_kvm_type;
     x86mc->save_tsc_khz = true;
     x86mc->fwcfg_dma_enabled = true;
     nc->nmi_monitor_handler = x86_nmi;

target/i386/confidential-guest.h

@@ -36,5 +36,24 @@ struct X86ConfidentialGuest {
 struct X86ConfidentialGuestClass {
     /* <private> */
     ConfidentialGuestSupportClass parent;
+
+    /* <public> */
+    int (*kvm_type)(X86ConfidentialGuest *cg);
 };
+
+/**
+ * x86_confidential_guest_kvm_type:
+ *
+ * Calls #X86ConfidentialGuestClass.unplug callback of @plug_handler.
+ */
+static inline int x86_confidential_guest_kvm_type(X86ConfidentialGuest *cg)
+{
+    X86ConfidentialGuestClass *klass = X86_CONFIDENTIAL_GUEST_GET_CLASS(cg);
+
+    if (klass->kvm_type) {
+        return klass->kvm_type(cg);
+    } else {
+        return 0;
+    }
+}
 #endif

target/i386/kvm/kvm.c

@@ -31,6 +31,7 @@
 #include "sysemu/kvm_int.h"
 #include "sysemu/runstate.h"
 #include "kvm_i386.h"
+#include "../confidential-guest.h"
 #include "sev.h"
 #include "xen-emu.h"
 #include "hyperv.h"
@@ -161,6 +162,49 @@ static KVMMSRHandlers msr_handlers[KVM_MSR_FILTER_MAX_RANGES];
 static RateLimit bus_lock_ratelimit_ctrl;
 static int kvm_get_one_msr(X86CPU *cpu, int index, uint64_t *value);
 
+static const char *vm_type_name[] = {
+    [KVM_X86_DEFAULT_VM] = "default",
+};
+
+bool kvm_is_vm_type_supported(int type)
+{
+    uint32_t machine_types;
+
+    /*
+     * old KVM doesn't support KVM_CAP_VM_TYPES but KVM_X86_DEFAULT_VM
+     * is always supported
+     */
+    if (type == KVM_X86_DEFAULT_VM) {
+        return true;
+    }
+
+    machine_types = kvm_check_extension(KVM_STATE(current_machine->accelerator),
+                                        KVM_CAP_VM_TYPES);
+    return !!(machine_types & BIT(type));
+}
+
+int kvm_get_vm_type(MachineState *ms)
+{
+    int kvm_type = KVM_X86_DEFAULT_VM;
+
+    if (ms->cgs) {
+        if (!object_dynamic_cast(OBJECT(ms->cgs), TYPE_X86_CONFIDENTIAL_GUEST)) {
+            error_report("configuration type %s not supported for x86 guests",
+                         object_get_typename(OBJECT(ms->cgs)));
+            exit(1);
+        }
+        kvm_type = x86_confidential_guest_kvm_type(
+            X86_CONFIDENTIAL_GUEST(ms->cgs));
+    }
+
+    if (!kvm_is_vm_type_supported(kvm_type)) {
+        error_report("vm-type %s not supported by KVM", vm_type_name[kvm_type]);
+        exit(1);
+    }
+
+    return kvm_type;
+}
+
 bool kvm_has_smm(void)
 {
     return kvm_vm_check_extension(kvm_state, KVM_CAP_X86_SMM);

target/i386/kvm/kvm_i386.h

@@ -37,6 +37,7 @@ bool kvm_hv_vpindex_settable(void);
 bool kvm_enable_sgx_provisioning(KVMState *s);
 bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
 
+int kvm_get_vm_type(MachineState *ms);
 void kvm_arch_reset_vcpu(X86CPU *cs);
 void kvm_arch_after_reset_vcpu(X86CPU *cpu);
 void kvm_arch_do_init_vcpu(X86CPU *cs);
@@ -49,6 +50,7 @@ void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask);
 
 #ifdef CONFIG_KVM
 
+bool kvm_is_vm_type_supported(int type);
 bool kvm_has_adjust_clock_stable(void);
 bool kvm_has_exception_payload(void);
 void kvm_synchronize_all_tsc(void);