[PATCH 1/4] KVM: arm64: Add helpers to halt a vCPU

[Oliver Upton <oupton@kernel.org>]

Currently we pause the entire VM when modifying VGIC state that requires
state to be synchronized back from hardware. This is perfectly fine for
heavyweight operations but not ideal for 'simple' things like migrating
an active/pending IRQ.

Add helpers for halting a single vCPU such that they can be used to
manipulate the AP list remotely.

Signed-off-by: Oliver Upton <oupton@kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  2 ++
 arch/arm64/kvm/arm.c              | 18 ++++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 66ea2372f987..48f536968a7d 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1254,6 +1254,8 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
 
 void kvm_arm_halt_guest(struct kvm *kvm);
 void kvm_arm_resume_guest(struct kvm *kvm);
+void kvm_pause_vcpu(struct kvm_vcpu *vcpu);
+void kvm_resume_vcpu(struct kvm_vcpu *vcpu);
 
 #define vcpu_has_run_once(vcpu)	(!!READ_ONCE((vcpu)->pid))
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index bbcaca8b36fb..9cf9b11a6457 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1023,15 +1023,25 @@ void kvm_arm_halt_guest(struct kvm *kvm)
 	kvm_make_all_cpus_request(kvm, KVM_REQ_SLEEP);
 }
 
+void kvm_pause_vcpu(struct kvm_vcpu *vcpu)
+{
+	atomic_inc(&vcpu->arch.pause);
+	kvm_make_request_and_kick(KVM_REQ_SLEEP, vcpu);
+}
+
+void kvm_resume_vcpu(struct kvm_vcpu *vcpu)
+{
+	if (atomic_dec_and_test(&vcpu->arch.pause))
+		__kvm_vcpu_wake_up(vcpu);
+}
+
 void kvm_arm_resume_guest(struct kvm *kvm)
 {
 	unsigned long i;
 	struct kvm_vcpu *vcpu;
 
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (atomic_dec_and_test(&vcpu->arch.pause))
-			__kvm_vcpu_wake_up(vcpu);
-	}
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		kvm_resume_vcpu(vcpu);
 }
 
 static void kvm_vcpu_sleep(struct kvm_vcpu *vcpu)
-- 
2.47.3