KVM: move EXIT_FASTPATH_REENTER_GUEST to common code

Now that KVM is using static calls, calling vmx_vcpu_run and
vmx_sync_pir_to_irr does not incur anymore the cost of a
retpoline.

Therefore there is no need anymore to handle EXIT_FASTPATH_REENTER_GUEST
in vendor code.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -6711,11 +6711,9 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 
 static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 {
-	fastpath_t exit_fastpath;
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long cr3, cr4;
 
-reenter_guest:
 	/* Record the guest's net vcpu time for enforced NMI injections. */
 	if (unlikely(!enable_vnmi &&
 		     vmx->loaded_vmcs->soft_vnmi_blocked))
@@ -6865,22 +6863,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	if (is_guest_mode(vcpu))
 		return EXIT_FASTPATH_NONE;
 
-	exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
-	if (exit_fastpath == EXIT_FASTPATH_REENTER_GUEST) {
-		if (!kvm_vcpu_exit_request(vcpu)) {
-			/*
-			 * FIXME: this goto should be a loop in vcpu_enter_guest,
-			 * but it would incur the cost of a retpoline for now.
-			 * Revisit once static calls are available.
-			 */
-			if (vcpu->arch.apicv_active)
-				vmx_sync_pir_to_irr(vcpu);
-			goto reenter_guest;
-		}
-		exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
-	}
-
-	return exit_fastpath;
+	return vmx_exit_handlers_fastpath(vcpu);
 }
 
 static void vmx_free_vcpu(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.c

@@ -1796,12 +1796,11 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
 
-bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
+static inline bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
 {
 	return vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu) ||
 		xfer_to_guest_mode_work_pending();
 }
-EXPORT_SYMBOL_GPL(kvm_vcpu_exit_request);
 
 /*
  * The fast path for frequent and performance sensitive wrmsr emulation,
@@ -9044,7 +9043,19 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
 	}
 
-	exit_fastpath = static_call(kvm_x86_run)(vcpu);
+	for (;;) {
+		exit_fastpath = static_call(kvm_x86_run)(vcpu);
+		if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
+			break;
+
+                if (unlikely(kvm_vcpu_exit_request(vcpu))) {
+			exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
+			break;
+		}
+
+		if (vcpu->arch.apicv_active)
+			static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+        }
 
 	/*
 	 * Do this here before restoring debug registers on the host.  And

arch/x86/kvm/x86.h

@@ -395,7 +395,6 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
 int kvm_spec_ctrl_test_value(u64 value);
 bool kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
-bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu);
 int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
 			      struct x86_exception *e);
 int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva);