KVM: x86: allow defining return-0 static calls

A few vendor callbacks are only used by VMX, but they return an integer
or bool value.  Introduce KVM_X86_OP_OPTIONAL_RET0 for them: if a func is
NULL in struct kvm_x86_ops, it will be changed to __static_call_return0
when updating static calls.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm-x86-ops.h

@@ -10,7 +10,9 @@ BUILD_BUG_ON(1)
  *
  * KVM_X86_OP_OPTIONAL() can be used for those functions that can have
  * a NULL definition, for example if "static_call_cond()" will be used
- * at the call sites.
+ * at the call sites.  KVM_X86_OP_OPTIONAL_RET0() can be used likewise
+ * to make a definition optional, but in this case the default will
+ * be __static_call_return0.
  */
 KVM_X86_OP(hardware_enable)
 KVM_X86_OP(hardware_disable)
@@ -77,15 +79,15 @@ KVM_X86_OP(check_apicv_inhibit_reasons)
 KVM_X86_OP(refresh_apicv_exec_ctrl)
 KVM_X86_OP_OPTIONAL(hwapic_irr_update)
 KVM_X86_OP_OPTIONAL(hwapic_isr_update)
-KVM_X86_OP_OPTIONAL(guest_apic_has_interrupt)
+KVM_X86_OP_OPTIONAL_RET0(guest_apic_has_interrupt)
 KVM_X86_OP_OPTIONAL(load_eoi_exitmap)
 KVM_X86_OP_OPTIONAL(set_virtual_apic_mode)
 KVM_X86_OP_OPTIONAL(set_apic_access_page_addr)
 KVM_X86_OP(deliver_interrupt)
 KVM_X86_OP_OPTIONAL(sync_pir_to_irr)
-KVM_X86_OP(set_tss_addr)
-KVM_X86_OP(set_identity_map_addr)
-KVM_X86_OP(get_mt_mask)
+KVM_X86_OP_OPTIONAL_RET0(set_tss_addr)
+KVM_X86_OP_OPTIONAL_RET0(set_identity_map_addr)
+KVM_X86_OP_OPTIONAL_RET0(get_mt_mask)
 KVM_X86_OP(load_mmu_pgd)
 KVM_X86_OP(has_wbinvd_exit)
 KVM_X86_OP(get_l2_tsc_offset)
@@ -103,7 +105,7 @@ KVM_X86_OP_OPTIONAL(vcpu_unblocking)
 KVM_X86_OP_OPTIONAL(pi_update_irte)
 KVM_X86_OP_OPTIONAL(pi_start_assignment)
 KVM_X86_OP_OPTIONAL(apicv_post_state_restore)
-KVM_X86_OP_OPTIONAL(dy_apicv_has_pending_interrupt)
+KVM_X86_OP_OPTIONAL_RET0(dy_apicv_has_pending_interrupt)
 KVM_X86_OP_OPTIONAL(set_hv_timer)
 KVM_X86_OP_OPTIONAL(cancel_hv_timer)
 KVM_X86_OP(setup_mce)
@@ -127,3 +129,4 @@ KVM_X86_OP(vcpu_deliver_sipi_vector)
 
 #undef KVM_X86_OP
 #undef KVM_X86_OP_OPTIONAL
+#undef KVM_X86_OP_OPTIONAL_RET0

arch/x86/include/asm/kvm_host.h

@@ -1541,6 +1541,7 @@ extern struct kvm_x86_ops kvm_x86_ops;
 #define KVM_X86_OP(func) \
 	DECLARE_STATIC_CALL(kvm_x86_##func, *(((struct kvm_x86_ops *)0)->func));
 #define KVM_X86_OP_OPTIONAL KVM_X86_OP
+#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
 #include <asm/kvm-x86-ops.h>
 
 static inline void kvm_ops_static_call_update(void)
@@ -1550,6 +1551,9 @@ static inline void kvm_ops_static_call_update(void)
 #define KVM_X86_OP(func) \
 	WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
 #define KVM_X86_OP_OPTIONAL __KVM_X86_OP
+#define KVM_X86_OP_OPTIONAL_RET0(func) \
+	static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
+			   (void *) __static_call_return0);
 #include <asm/kvm-x86-ops.h>
 #undef __KVM_X86_OP
 }

arch/x86/kvm/svm/avic.c

@@ -650,11 +650,6 @@ void avic_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
 	avic_set_pi_irte_mode(vcpu, activated);
 }
 
-bool avic_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu)
-{
-	return false;
-}
-
 static void svm_ir_list_del(struct vcpu_svm *svm, struct amd_iommu_pi_data *pi)
 {
 	unsigned long flags;

arch/x86/kvm/svm/svm.c

@@ -3528,16 +3528,6 @@ static void svm_enable_nmi_window(struct kvm_vcpu *vcpu)
 	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
 }
 
-static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
-{
-	return 0;
-}
-
-static int svm_set_identity_map_addr(struct kvm *kvm, u64 ident_addr)
-{
-	return 0;
-}
-
 static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -3934,11 +3924,6 @@ static bool svm_has_emulated_msr(struct kvm *kvm, u32 index)
 	return true;
 }
 
-static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
-{
-	return 0;
-}
-
 static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -4593,10 +4578,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.check_apicv_inhibit_reasons = avic_check_apicv_inhibit_reasons,
 	.apicv_post_state_restore = avic_apicv_post_state_restore,
 
-	.set_tss_addr = svm_set_tss_addr,
-	.set_identity_map_addr = svm_set_identity_map_addr,
-	.get_mt_mask = svm_get_mt_mask,
-
 	.get_exit_info = svm_get_exit_info,
 
 	.vcpu_after_set_cpuid = svm_vcpu_after_set_cpuid,
@@ -4621,7 +4602,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.nested_ops = &svm_nested_ops,
 
 	.deliver_interrupt = svm_deliver_interrupt,
-	.dy_apicv_has_pending_interrupt = avic_dy_apicv_has_pending_interrupt,
 	.pi_update_irte = avic_pi_update_irte,
 	.setup_mce = svm_setup_mce,
 

arch/x86/kvm/x86.c

@@ -131,6 +131,7 @@ struct kvm_x86_ops kvm_x86_ops __read_mostly;
 	DEFINE_STATIC_CALL_NULL(kvm_x86_##func,			     \
 				*(((struct kvm_x86_ops *)0)->func));
 #define KVM_X86_OP_OPTIONAL KVM_X86_OP
+#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
 #include <asm/kvm-x86-ops.h>
 EXPORT_STATIC_CALL_GPL(kvm_x86_get_cs_db_l_bits);
 EXPORT_STATIC_CALL_GPL(kvm_x86_cache_reg);
@@ -12016,8 +12017,7 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 static inline bool kvm_guest_apic_has_interrupt(struct kvm_vcpu *vcpu)
 {
 	return (is_guest_mode(vcpu) &&
-			kvm_x86_ops.guest_apic_has_interrupt &&
-			static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));
+		static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));
 }
 
 static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)

kernel/static_call.c

@@ -503,6 +503,7 @@ long __static_call_return0(void)
 {
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__static_call_return0);
 
 #ifdef CONFIG_STATIC_CALL_SELFTEST