i386/tdx: Implement tdx_kvm_init() to initialize TDX VM context

Introduce tdx_kvm_init() and invoke it in kvm_confidential_guest_init()
if it's a TDX VM.

Set ms->require_guest_memfd to require kvm guest memfd allocation for any
memory backend. More TDX specific initialization will be added later.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

target/i386/kvm/kvm.c

@@ -62,6 +62,7 @@
 #include "migration/blocker.h"
 #include "exec/memattrs.h"
 #include "trace.h"
+#include "tdx.h"
 
 #include CONFIG_DEVICES
 
@@ -2546,6 +2547,8 @@ static int kvm_confidential_guest_init(MachineState *ms, Error **errp)
 {
     if (object_dynamic_cast(OBJECT(ms->cgs), TYPE_SEV_GUEST)) {
         return sev_kvm_init(ms->cgs, errp);
+    } else if (object_dynamic_cast(OBJECT(ms->cgs), TYPE_TDX_GUEST)) {
+        return tdx_kvm_init(ms, errp);
     }
 
     return 0;
@@ -2560,16 +2563,10 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     Error *local_err = NULL;
 
     /*
-     * Initialize SEV context, if required
+     * Initialize confidential guest (SEV/TDX) context, if required
      *
-     * If no memory encryption is requested (ms->cgs == NULL) this is
-     * a no-op.
-     *
-     * It's also a no-op if a non-SEV confidential guest support
-     * mechanism is selected.  SEV is the only mechanism available to
-     * select on x86 at present, so this doesn't arise, but if new
-     * mechanisms are supported in future (e.g. TDX), they'll need
-     * their own initialization either here or elsewhere.
+     * It's a no-op if a non-SEV/non-tdx confidential guest support
+     * mechanism is selected, i.e., ms->cgs == NULL
      */
     ret = kvm_confidential_guest_init(ms, &local_err);
     if (ret < 0) {

target/i386/kvm/meson.build

@@ -9,7 +9,7 @@ i386_kvm_ss.add(when: 'CONFIG_XEN_EMU', if_true: files('xen-emu.c'))
 
 i386_kvm_ss.add(when: 'CONFIG_SEV', if_false: files('sev-stub.c'))
 
-i386_kvm_ss.add(when: 'CONFIG_TDX', if_true: files('tdx.c'))
+i386_kvm_ss.add(when: 'CONFIG_TDX', if_true: files('tdx.c'), if_false: files('tdx-stub.c'))
 
 i386_system_ss.add(when: 'CONFIG_HYPERV', if_true: files('hyperv.c'), if_false: files('hyperv-stub.c'))
 

target/i386/kvm/tdx-stub.c

@@ -0,0 +1,8 @@
+#include "qemu/osdep.h"
+
+#include "tdx.h"
+
+int tdx_kvm_init(MachineState *ms, Error **errp)
+{
+    return -EINVAL;
+}

target/i386/kvm/tdx.c

@@ -12,10 +12,19 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 #include "qom/object_interfaces.h"
 
+#include "hw/i386/x86.h"
 #include "tdx.h"
 
+int tdx_kvm_init(MachineState *ms, Error **errp)
+{
+    ms->require_guest_memfd = true;
+
+    return 0;
+}
+
 /* tdx guest */
 OBJECT_DEFINE_TYPE_WITH_INTERFACES(TdxGuest,
                                    tdx_guest,

target/i386/kvm/tdx.h

@@ -16,4 +16,6 @@ typedef struct TdxGuest {
     uint64_t attributes;    /* TD attributes */
 } TdxGuest;
 
+int tdx_kvm_init(MachineState *ms, Error **errp);
+
 #endif /* QEMU_I386_TDX_H */