KVM: TDX: Always block INIT/SIPI

Always block INIT and SIPI events for the TDX guest because the TDX module
doesn't provide API for VMM to inject INIT IPI or SIPI.

TDX defines its own vCPU creation and initialization sequence including
multiple seamcalls.  Also, it's only allowed during TD build time.

Given that TDX guest is para-virtualized to boot BSP/APs, normally there
shouldn't be any INIT/SIPI event for TDX guest.  If any, three options to
handle them:
1. Always block INIT/SIPI request.
2. (Silently) ignore INIT/SIPI request during delivery.
3. Return error to guest TDs somehow.

Choose option 1 for simplicity. Since INIT and SIPI are always blocked,
INIT handling and the OP vcpu_deliver_sipi_vector() won't be called, no
need to add new interface or helper function for INIT/SIPI delivery.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20250222014757.897978-10-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: yamahata

arch/x86/kvm/vmx/main.c

@@ -118,8 +118,10 @@ static void vt_vcpu_free(struct kvm_vcpu *vcpu)
 
 static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
-	if (is_td_vcpu(vcpu))
+	if (is_td_vcpu(vcpu)) {
+		tdx_vcpu_reset(vcpu, init_event);
 		return;
+	}
 
 	vmx_vcpu_reset(vcpu, init_event);
 }
@@ -226,6 +228,18 @@ static void vt_enable_smi_window(struct kvm_vcpu *vcpu)
 }
 #endif
 
+static bool vt_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * INIT and SIPI are always blocked for TDX, i.e., INIT handling and
+	 * the OP vcpu_deliver_sipi_vector() won't be called.
+	 */
+	if (is_td_vcpu(vcpu))
+		return true;
+
+	return vmx_apic_init_signal_blocked(vcpu);
+}
+
 static void vt_apicv_pre_state_restore(struct kvm_vcpu *vcpu)
 {
 	struct pi_desc *pi = vcpu_to_pi_desc(vcpu);
@@ -591,7 +605,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 #endif
 
 	.check_emulate_instruction = vmx_check_emulate_instruction,
-	.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
+	.apic_init_signal_blocked = vt_apic_init_signal_blocked,
 	.migrate_timers = vmx_migrate_timers,
 
 	.msr_filter_changed = vmx_msr_filter_changed,

arch/x86/kvm/vmx/tdx.c

@@ -2626,6 +2626,19 @@ static int tdx_vcpu_init(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *cmd)
 	return 0;
 }
 
+void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
+{
+	/*
+	 * Yell on INIT, as TDX doesn't support INIT, i.e. KVM should drop all
+	 * INIT events.
+	 *
+	 * Defer initializing vCPU for RESET state until KVM_TDX_INIT_VCPU, as
+	 * userspace needs to define the vCPU model before KVM can initialize
+	 * vCPU state, e.g. to enable x2APIC.
+	 */
+	WARN_ON_ONCE(init_event);
+}
+
 struct tdx_gmem_post_populate_arg {
 	struct kvm_vcpu *vcpu;
 	__u32 flags;

arch/x86/kvm/vmx/x86_ops.h

@@ -128,6 +128,7 @@ void tdx_vm_destroy(struct kvm *kvm);
 int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
 
 int tdx_vcpu_create(struct kvm_vcpu *vcpu);
+void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
 void tdx_vcpu_free(struct kvm_vcpu *vcpu);
 void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
 int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu);
@@ -167,6 +168,7 @@ static inline void tdx_vm_destroy(struct kvm *kvm) {}
 static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
 
 static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
+static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
 static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
 static inline void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {}
 static inline int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }