From: Marc-André Lureau <marcandre.lureau@redhat.com>

Return an empty TdxCapability struct, for extensibility and matching
query-sev-capabilities return type.

Fixes: https://issues.redhat.com/browse/RHEL-129674
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 qapi/misc-i386.json        | 30 ++++++++++++++++++++++++++++++
 target/i386/kvm/kvm_i386.h |  1 +
 target/i386/kvm/kvm.c      |  5 +++++
 target/i386/kvm/tdx-stub.c |  8 ++++++++
 target/i386/kvm/tdx.c      | 21 +++++++++++++++++++++
 5 files changed, 65 insertions(+)

diff --git a/qapi/misc-i386.json b/qapi/misc-i386.json
index 05a94d6c416..f10e4338b48 100644
--- a/qapi/misc-i386.json
+++ b/qapi/misc-i386.json
@@ -225,6 +225,36 @@
 ##
 { 'command': 'query-sev-capabilities', 'returns': 'SevCapability' }
 
+##
+# @TdxCapability:
+#
+# The struct describes capability for Intel Trust Domain Extensions
+# (TDX) feature.
+#
+# Since: 11.0
+##
+{ 'struct': 'TdxCapability',
+  'data': { } }
+
+##
+# @query-tdx-capabilities:
+#
+# Get TDX capabilities.
+#
+# This is only supported on Intel X86 platforms with KVM enabled.
+#
+# Errors:
+#     - If TDX is not available on the platform, GenericError
+#
+# Since: 11.0
+#
+# .. qmp-example::
+#
+#     -> { "execute": "query-tdx-capabilities" }
+#     <- { "return": {} }
+##
+{ 'command': 'query-tdx-capabilities', 'returns': 'TdxCapability' }
+
 ##
 # @sev-inject-launch-secret:
 #
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index 2b653442f4d..71dd45be47a 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -61,6 +61,7 @@ void kvm_put_apicbase(X86CPU *cpu, uint64_t value);
 
 bool kvm_has_x2apic_api(void);
 bool kvm_has_waitpkg(void);
+bool kvm_has_tdx(void);
 
 uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
 void kvm_update_msi_routes_all(void *private, bool global,
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 7b9b740a8e5..8ce25d7e785 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -6582,6 +6582,11 @@ bool kvm_has_waitpkg(void)
     return has_msr_umwait;
 }
 
+bool kvm_has_tdx(void)
+{
+    return kvm_is_vm_type_supported(KVM_X86_TDX_VM);
+}
+
 #define ARCH_REQ_XCOMP_GUEST_PERM       0x1025
 
 void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask)
diff --git a/target/i386/kvm/tdx-stub.c b/target/i386/kvm/tdx-stub.c
index 1f0e108a69e..c4e7f2c58c8 100644
--- a/target/i386/kvm/tdx-stub.c
+++ b/target/i386/kvm/tdx-stub.c
@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-misc-i386.h"
 
 #include "tdx.h"
 
@@ -30,3 +32,9 @@ void tdx_handle_get_tdvmcall_info(X86CPU *cpu, struct kvm_run *run)
 void tdx_handle_setup_event_notify_interrupt(X86CPU *cpu, struct kvm_run *run)
 {
 }
+
+TdxCapability *qmp_query_tdx_capabilities(Error **errp)
+{
+    error_setg(errp, "TDX is not available in this QEMU");
+    return NULL;
+}
diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index 01619857685..b5ee3b1ab92 100644
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -14,6 +14,7 @@
 #include "qemu/base64.h"
 #include "qemu/mmap-alloc.h"
 #include "qapi/error.h"
+#include "qapi/qapi-commands-misc-i386.h"
 #include "qapi/qapi-visit-sockets.h"
 #include "qom/object_interfaces.h"
 #include "crypto/hash.h"
@@ -1537,6 +1538,26 @@ static void tdx_guest_finalize(Object *obj)
 {
 }
 
+static TdxCapability *tdx_get_capabilities(Error **errp)
+{
+    if (!kvm_enabled()) {
+        error_setg(errp, "TDX is not available without KVM");
+        return NULL;
+    }
+
+    if (!kvm_has_tdx()) {
+        error_setg(errp, "TDX is not supported by this host");
+        return NULL;
+    }
+
+    return g_new0(TdxCapability, 1);
+}
+
+TdxCapability *qmp_query_tdx_capabilities(Error **errp)
+{
+    return tdx_get_capabilities(errp);
+}
+
 static void tdx_guest_class_init(ObjectClass *oc, const void *data)
 {
     ConfidentialGuestSupportClass *klass = CONFIDENTIAL_GUEST_SUPPORT_CLASS(oc);
-- 
2.52.0