i386/tdx: Disable SMM for TDX VMs

TDX doesn't support SMM and VMM cannot emulate SMM for TDX VMs because
VMM cannot manipulate TDX VM's memory.

Disable SMM for TDX VMs and error out if user requests to enable SMM.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-37-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index 344e560b4b877df2de6a1e58e47df25ae950bb83..87c5bf04960f1996700f6ecf1629088bbbf1081a 100644 (file)
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -367,11 +367,20 @@ static Notifier tdx_machine_done_notify = {
 
 static int tdx_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
 {
+    MachineState *ms = MACHINE(qdev_get_machine());
+    X86MachineState *x86ms = X86_MACHINE(ms);
     TdxGuest *tdx = TDX_GUEST(cgs);
     int r = 0;
 
     kvm_mark_guest_state_protected();
 
+    if (x86ms->smm == ON_OFF_AUTO_AUTO) {
+        x86ms->smm = ON_OFF_AUTO_OFF;
+    } else if (x86ms->smm == ON_OFF_AUTO_ON) {
+        error_setg(errp, "TDX VM doesn't support SMM");
+        return -EINVAL;
+    }
+
     if (!tdx_caps) {
         r = get_tdx_capabilities(errp);
         if (r) {