ARM/ARM64: KVM: Emulate PSCI v0.2 CPU_SUSPEND

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/)

For simplicity, 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 consistent with section
5.4.1 and section 5.4.2 of PSCI v0.2 specification.

Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

1 files changed, 24 insertions, 4 deletions

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
index 1067579c7336..09cf37737ee2 100644
--- a/arch/arm/kvm/psci.c
+++ b/arch/arm/kvm/psci.c
@@ -37,6 +37,26 @@ 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);
+
+        return PSCI_RET_SUCCESS;
+}
+
 static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
 {
         vcpu->arch.pause = true;
@@ -183,6 +203,10 @@ 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;
@@ -235,10 +259,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
                 val = PSCI_RET_INTERNAL_FAILURE;
                 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;
         }