[PATCH 5/7] KVM: arm64: Add helpers to halt a vCPU

[Marc Zyngier]

From: Oliver Upton <oupton at 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 at kernel.org>
Link: https://patch.msgid.link/20260929212925.31775-2-oupton@kernel.org
[maz: fixed to use kvm_make_vcpus_request_mask(), guaranteeing that the
      caller waits for the target vcpu to handle the IPI]
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  2 ++
 arch/arm64/kvm/arm.c              | 21 +++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9c068f27f9b8a..7b4f7b6d94b8d 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 07bf8b2e683d5..a2f1606822614 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1017,6 +1017,21 @@ bool kvm_arch_intc_initialized(struct kvm *kvm)
 	return vgic_initialized(kvm);
 }
 
+void kvm_pause_vcpu(struct kvm_vcpu *vcpu)
+{
+	DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS) = { };
+
+	atomic_inc(&vcpu->arch.pause);
+	__set_bit(vcpu->vcpu_idx, vcpu_bitmap);
+	kvm_make_vcpus_request_mask(vcpu->kvm, KVM_REQ_SLEEP, vcpu_bitmap);
+}
+
+void kvm_resume_vcpu(struct kvm_vcpu *vcpu)
+{
+	if (atomic_dec_and_test(&vcpu->arch.pause))
+		__kvm_vcpu_wake_up(vcpu);
+}
+
 void kvm_arm_halt_guest(struct kvm *kvm)
 {
 	unsigned long i;
@@ -1032,10 +1047,8 @@ 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