[PATCH 2/5] KVM: arm/arm64: replace vcpu->arch.pause with a vcpu-request

[Andrew Jones <drjones@redhat.com>]

This not only ensures visibility of changes to pause by using
atomic ops, but also plugs a small race where a vcpu could get
its pause state enabled just after its last check before entering
the guest. With this patch, while the vcpu will still initially
enter the guest, it will exit immediately due to the IPI sent by
the vcpu kick issued after making the vcpu request.

We use __kvm_request_set, because we don't need the barrier
kvm_request_set() provides. Additionally, kvm_request_test_and_clear
is not used because, for pause, only the requester should do the
clearing, i.e. testing and clearing need to be independent.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 arch/arm/include/asm/kvm_host.h   |  5 +----
 arch/arm/kvm/arm.c                | 26 +++++++++++++-------------
 arch/arm64/include/asm/kvm_host.h |  5 +----
 3 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index cc495d799c67..3b5d60611cac 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -46,7 +46,7 @@
 #define KVM_MAX_VCPUS VGIC_V2_MAX_CPUS
 #endif
 
-#define KVM_REQ_VCPU_EXIT	8
+#define KVM_REQ_VCPU_PAUSE	8
 
 u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
 int __attribute_const__ kvm_target_cpu(void);
@@ -174,9 +174,6 @@ struct kvm_vcpu_arch {
 	/* vcpu power-off state */
 	bool power_off;
 
-	 /* Don't run the guest (internal implementation need) */
-	bool pause;
-
 	/* IO related fields */
 	struct kvm_decode mmio_decode;
 
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index c9a2103faeb9..17d5f3fb33d9 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -401,7 +401,8 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
 {
 	return ((!!v->arch.irq_lines || kvm_vgic_vcpu_pending_irq(v))
-		&& !v->arch.power_off && !v->arch.pause);
+		&& !v->arch.power_off
+		&& !__kvm_request_test(KVM_REQ_VCPU_PAUSE, v));
 }
 
 /* Just ensure a guest exit from a particular CPU */
@@ -532,17 +533,12 @@ bool kvm_arch_intc_initialized(struct kvm *kvm)
 
 void kvm_arm_halt_guest(struct kvm *kvm)
 {
-	int i;
-	struct kvm_vcpu *vcpu;
-
-	kvm_for_each_vcpu(i, vcpu, kvm)
-		vcpu->arch.pause = true;
-	kvm_make_all_cpus_request(kvm, KVM_REQ_VCPU_EXIT);
+	kvm_make_all_cpus_request(kvm, KVM_REQ_VCPU_PAUSE);
 }
 
 void kvm_arm_halt_vcpu(struct kvm_vcpu *vcpu)
 {
-	vcpu->arch.pause = true;
+	__kvm_request_set(KVM_REQ_VCPU_PAUSE, vcpu);
 	kvm_vcpu_kick(vcpu);
 }
 
@@ -550,7 +546,7 @@ void kvm_arm_resume_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct swait_queue_head *wq = kvm_arch_vcpu_wq(vcpu);
 
-	vcpu->arch.pause = false;
+	__kvm_request_clear(KVM_REQ_VCPU_PAUSE, vcpu);
 	swake_up(wq);
 }
 
@@ -568,7 +564,7 @@ static void vcpu_sleep(struct kvm_vcpu *vcpu)
 	struct swait_queue_head *wq = kvm_arch_vcpu_wq(vcpu);
 
 	swait_event_interruptible(*wq, ((!vcpu->arch.power_off) &&
-				       (!vcpu->arch.pause)));
+		(!__kvm_request_test(KVM_REQ_VCPU_PAUSE, vcpu))));
 }
 
 static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
@@ -621,7 +617,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
 		update_vttbr(vcpu->kvm);
 
-		if (vcpu->arch.power_off || vcpu->arch.pause)
+		if (vcpu->arch.power_off || __kvm_request_test(KVM_REQ_VCPU_PAUSE, vcpu))
 			vcpu_sleep(vcpu);
 
 		/*
@@ -644,8 +640,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			run->exit_reason = KVM_EXIT_INTR;
 		}
 
+		vcpu->mode = IN_GUEST_MODE;
+		smp_mb(); /* ensure vcpu->mode is visible to kvm_vcpu_kick */
+
 		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
-			vcpu->arch.power_off || vcpu->arch.pause) {
+			vcpu->arch.power_off || kvm_request_pending(vcpu)) {
+			vcpu->mode = OUTSIDE_GUEST_MODE;
+			smp_mb();
 			local_irq_enable();
 			kvm_pmu_sync_hwstate(vcpu);
 			kvm_timer_sync_hwstate(vcpu);
@@ -661,7 +662,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		 */
 		trace_kvm_entry(*vcpu_pc(vcpu));
 		guest_enter_irqoff();
-		vcpu->mode = IN_GUEST_MODE;
 
 		ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f21fd3894370..c03e1fc3bc34 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -43,7 +43,7 @@
 
 #define KVM_VCPU_MAX_FEATURES 4
 
-#define KVM_REQ_VCPU_EXIT	8
+#define KVM_REQ_VCPU_PAUSE	8
 
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
@@ -257,9 +257,6 @@ struct kvm_vcpu_arch {
 	/* vcpu power-off state */
 	bool power_off;
 
-	/* Don't run the guest (internal implementation need) */
-	bool pause;
-
 	/* IO related fields */
 	struct kvm_decode mmio_decode;
 
-- 
2.9.3