[PATCH v7 11/12] ARM/ARM64: KVM: Emulate PSCI v0.2 CPU_SUSPEND

[Anup Patel]

This patch adds emulation of PSCI v0.2 CPU_SUSPEND function call for
KVM ARM/ARM64. This is a CPU-level function call which can suspend
current CPU or current CPU cluster. We don't have VCPU clusters in
KVM so we only suspend the current VCPU.

The CPU_SUSPEND emulation is not tested much because currently there
is no CPUIDLE driver in Linux kernel that uses PSCI CPU_SUSPEND. The
PSCI CPU_SUSPEND implementation in ARM64 kernel was tested using a
Simple CPUIDLE driver which is not published due to unstable DT-bindings
for PSCI.
(For more info, http://lwn.net/Articles/574950/)

Even if we had stable DT-bindings for PSCI and CPUIDLE driver that
uses PSCI CPU_SUSPEND then still we need to define SUSPEND states
and WAKEUP events for KVM ARM/ARM64.

Due to above, we implement CPU_SUSPEND emulation similar to WFI
(Wait-for-interrupt) emulation and we also treat power-down request
to be same as stand-by request. This is also consistent with section
5.4.1 and section 5.4.2 of PSCI v0.2 specification.

Signed-off-by: Anup Patel <anup.patel at linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar at linaro.org>
---
 arch/arm/kvm/psci.c |   27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
index fdbd829..74fa4ad 100644
--- a/arch/arm/kvm/psci.c
+++ b/arch/arm/kvm/psci.c
@@ -52,6 +52,25 @@ static unsigned long psci_affinity_mask(unsigned long affinity_level)
 	return affinity_mask;
 }
 
+static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * NOTE: Currently, we don't have any wakeup events for KVM
+	 * so for simplicity we make VCPU suspend emulation to be
+	 * same-as WFI (Wait-for-interrupt) emulation. This is also
+	 * 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 PSCI emulation will preserve the register state.
+	 */
+	kvm_vcpu_block(vcpu);
+
+	return PSCI_RET_SUCCESS;
+}
+
 static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.pause = true;
@@ -195,6 +214,10 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 		 */
 		val = 2;
 		break;
+	case PSCI_0_2_FN_CPU_SUSPEND:
+	case PSCI_0_2_FN64_CPU_SUSPEND:
+		val = kvm_psci_vcpu_suspend(vcpu);
+		break;
 	case PSCI_0_2_FN_CPU_OFF:
 		kvm_psci_vcpu_off(vcpu);
 		val = PSCI_RET_SUCCESS;
@@ -232,10 +255,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 		val = PSCI_RET_SUCCESS;
 		ret = 0;
 		break;
-	case PSCI_0_2_FN_CPU_SUSPEND:
-	case PSCI_0_2_FN64_CPU_SUSPEND:
-		val = PSCI_RET_NOT_SUPPORTED;
-		break;
 	default:
 		return -EINVAL;
 	}
-- 
1.7.9.5