linux-kernel - [PATCH] RISCV: KVM: Add support for userspace to suspend a vCPU

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Message-ID: <20250918073927.403410-1-qiaozhe@iscas.ac.cn>
Date: Thu, 18 Sep 2025 15:39:27 +0800
From: Zhe Qiao <qiaozhe@...as.ac.cn>
To: anup@...infault.org,
	atish.patra@...ux.dev,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	qiaozhe@...as.ac.cn
Cc: linux-riscv@...ts.infradead.org,
	kvm-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: [PATCH] RISCV: KVM: Add support for userspace to suspend a vCPU

Add RISC-V architecture support for the KVM_MP_STATE_SUSPENDED vCPU
state, indicating that a vCPU is in suspended mode. While suspended,
the vCPU will block execution until a wakeup event is detected.

Introduce a new system event type, KVM_SYSTEM_EVENT_WAKEUP, to notify
userspace when KVM has recognized such a wakeup event. It is then
userspace’s responsibility to either make the vCPU runnable again or
keep it suspended until the next wakeup event occurs.

Signed-off-by: Zhe Qiao <qiaozhe@...as.ac.cn>
---
 arch/riscv/include/asm/kvm_host.h |  2 ++
 arch/riscv/kvm/vcpu.c             | 37 +++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index d71d3299a335..dbc6391407ae 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -43,6 +43,8 @@
 #define KVM_REQ_HFENCE			\
 	KVM_ARCH_REQ_FLAGS(5, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_STEAL_UPDATE		KVM_ARCH_REQ(6)
+#define KVM_REQ_SUSPEND		\
+	KVM_ARCH_REQ_FLAGS(7, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 
 #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
 
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 3ebcfffaa978..0881c78476b1 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -496,6 +496,18 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static void kvm_riscv_vcpu_suspend(struct kvm_vcpu *vcpu)
+{
+	WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_SUSPENDED);
+	kvm_make_request(KVM_REQ_SUSPEND, vcpu);
+	kvm_vcpu_kick(vcpu);
+}
+
+static bool kvm_riscv_vcpu_suspended(struct kvm_vcpu *vcpu)
+{
+	return READ_ONCE(vcpu->arch.mp_state.mp_state) == KVM_MP_STATE_SUSPENDED;
+}
+
 int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 				    struct kvm_mp_state *mp_state)
 {
@@ -516,6 +528,9 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 		else
 			ret = -EINVAL;
 		break;
+	case KVM_MP_STATE_SUSPENDED:
+		kvm_riscv_vcpu_suspend(vcpu);
+		break;
 	default:
 		ret = -EINVAL;
 	}
@@ -682,6 +697,25 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	}
 }
 
+static int kvm_riscv_handle_suspend(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_riscv_vcpu_suspended(vcpu))
+		return 1;
+
+	kvm_riscv_vcpu_wfi(vcpu);
+
+	kvm_make_request(KVM_REQ_SUSPEND, vcpu);
+
+	if (kvm_arch_vcpu_runnable(vcpu)) {
+		memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event));
+		vcpu->run->system_event.type = KVM_SYSTEM_EVENT_WAKEUP;
+		vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
+		return 0;
+	}
+
+	return 1;
+}
+
 /**
  * kvm_riscv_check_vcpu_requests - check and handle pending vCPU requests
  * @vcpu:	the VCPU pointer
@@ -731,6 +765,9 @@ static int kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
 		if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
 			kvm_riscv_vcpu_record_steal_time(vcpu);
 
+		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
+			kvm_riscv_handle_suspend(vcpu);
+
 		if (kvm_dirty_ring_check_request(vcpu))
 			return 0;
 	}
-- 
2.43.0