[RFC PATCH 2/5] KVM: arm64: Move WFI execution to check_vcpu_requests()

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Prepare for WFI requests from userspace, by adding a suspend request and
moving the WFI execution into check_vcpu_requests(), next to the
power-off logic.

vcpu->arch.mp_state, previously only RUNNABLE or STOPPED, supports an
additional state HALTED and two new state transitions:

  RUNNABLE -> HALTED	from WFI or PSCI CPU_SUSPEND (same vCPU)
  HALTED -> RUNNABLE	vGIC IRQ, pending timer, signal

There shouldn't be any functional change with this patch, even though
the KVM_GET_MP_STATE ioctl could now in theory return
KVM_MP_STATE_HALTED, which would break some users' mp_state support. In
practice it should not happen because we do not return to userspace with
HALTED state. Both WFI and PSCI CPU_SUSPEND stay in the vCPU run loop
until the suspend request is consumed. It does feel fragile though,
maybe we should explicitly return RUNNABLE in KVM_GET_MP_STATE in place
of HALTED, to prevent future breakage.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
 arch/arm64/include/asm/kvm_host.h |  2 ++
 arch/arm64/kvm/arm.c              | 18 ++++++++++++++-
 arch/arm64/kvm/handle_exit.c      |  3 +--
 arch/arm64/kvm/psci.c             | 37 +++++++++++++------------------
 4 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 55a04f4d5919..3ca732feb9a5 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -46,6 +46,7 @@
 #define KVM_REQ_VCPU_RESET	KVM_ARCH_REQ(2)
 #define KVM_REQ_RECORD_STEAL	KVM_ARCH_REQ(3)
 #define KVM_REQ_RELOAD_GICv4	KVM_ARCH_REQ(4)
+#define KVM_REQ_SUSPEND		KVM_ARCH_REQ(5)
 
 #define KVM_DIRTY_LOG_MANUAL_CAPS   (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
 				     KVM_DIRTY_LOG_INITIALLY_SET)
@@ -722,6 +723,7 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
 			       struct kvm_device_attr *attr);
 void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu);
 bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu);
+void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu);
 
 /* Guest/host FPSIMD coordination helpers */
 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index bcc24adb9c0a..d8cbaa0373c7 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -447,6 +447,12 @@ bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu)
 	return vcpu->arch.mp_state == KVM_MP_STATE_STOPPED;
 }
 
+void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
+	kvm_make_request(KVM_REQ_SUSPEND, vcpu);
+}
+
 int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
 				    struct kvm_mp_state *mp_state)
 {
@@ -667,6 +673,8 @@ static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
 
 static void check_vcpu_requests(struct kvm_vcpu *vcpu)
 {
+	bool irq_pending;
+
 	if (kvm_request_pending(vcpu)) {
 		if (kvm_check_request(KVM_REQ_SLEEP, vcpu))
 			vcpu_req_sleep(vcpu);
@@ -678,7 +686,7 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
 		 * Clear IRQ_PENDING requests that were made to guarantee
 		 * that a VCPU sees new virtual interrupts.
 		 */
-		kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
+		irq_pending = kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
 
 		if (kvm_check_request(KVM_REQ_RECORD_STEAL, vcpu))
 			kvm_update_stolen_time(vcpu);
@@ -690,6 +698,14 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
 			vgic_v4_load(vcpu);
 			preempt_enable();
 		}
+
+		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu)) {
+			if (!irq_pending) {
+				kvm_vcpu_block(vcpu);
+				kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+			}
+			vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
+		}
 	}
 }
 
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 6f48336b1d86..9717df3104cf 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -95,8 +95,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
 	} else {
 		trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
 		vcpu->stat.wfi_exit_stat++;
-		kvm_vcpu_block(vcpu);
-		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+		kvm_arm_vcpu_suspend(vcpu);
 	}
 
 	kvm_incr_pc(vcpu);
diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
index 24b4a2265dbd..42a307ceb95f 100644
--- a/arch/arm64/kvm/psci.c
+++ b/arch/arm64/kvm/psci.c
@@ -31,27 +31,6 @@ static unsigned long psci_affinity_mask(unsigned long affinity_level)
 	return 0;
 }
 
-static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
-{
-	/*
-	 * NOTE: For simplicity, we make VCPU suspend emulation to be
-	 * same-as WFI (Wait-for-interrupt) emulation.
-	 *
-	 * This means for KVM the wakeup events are interrupts and
-	 * this is consistent with intended use of StateID as described
-	 * in section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
-	 *
-	 * Further, we also treat power-down request to be same as
-	 * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
-	 * specification (ARM DEN 0022A). This means all suspend states
-	 * for KVM will preserve the register state.
-	 */
-	kvm_vcpu_block(vcpu);
-	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
-
-	return PSCI_RET_SUCCESS;
-}
-
 static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
 {
 	struct vcpu_reset_state *reset_state;
@@ -227,7 +206,21 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 		break;
 	case PSCI_0_2_FN_CPU_SUSPEND:
 	case PSCI_0_2_FN64_CPU_SUSPEND:
-		val = kvm_psci_vcpu_suspend(vcpu);
+		/*
+		 * NOTE: For simplicity, we make VCPU suspend emulation to be
+		 * same-as WFI (Wait-for-interrupt) emulation.
+		 *
+		 * This means for KVM the wakeup events are interrupts and this
+		 * is consistent with intended use of StateID as described in
+		 * section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
+		 *
+		 * Further, we also treat power-down request to be same as
+		 * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
+		 * specification (ARM DEN 0022A). This means all suspend states
+		 * for KVM will preserve the register state.
+		 */
+		kvm_arm_vcpu_suspend(vcpu);
+		val = PSCI_RET_SUCCESS;
 		break;
 	case PSCI_0_2_FN_CPU_OFF:
 		kvm_arm_vcpu_power_off(vcpu);
-- 
2.31.1