On 22 March 2014 05:07, Christoffer Dall [off-list ref] wrote:

On Fri, Mar 21, 2014 at 06:23:33PM +0530, Anup Patel wrote:

quoted

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 for KVM we simply 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
for KVM ARM/ARM64.

Due to this, the CPU_SUSPEND emulation added by this patch only pause
current VCPU and to wakeup a suspended VCPU we need to explicity call
PSCI CPU_ON from Guest.

Signed-off-by: Anup Patel <redacted>
Signed-off-by: Pranavkumar Sawargaonkar <redacted>
---
 arch/arm/kvm/psci.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
index 1e85452..e32ad10 100644
--- a/arch/arm/kvm/psci.c
+++ b/arch/arm/kvm/psci.c

@@ -52,6 +52,22 @@ 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
+      * hence VCPU suspend turns-out to be same as VCPU off request.
+      * This means to suspend a VCPU we simply set the pause flag
+      * and update VCPU registers as-per wakeup parameters provided
+      * via r2 & r3 (or x2 & x3).
+      */
+     vcpu->arch.pause = true;
+     *vcpu_pc(vcpu) = *vcpu_reg(vcpu, 2);
+     *vcpu_reg(vcpu, 0) = *vcpu_reg(vcpu, 3);

But the spec states in Section 5.1.2 that if Bit[16] StateType == 0,
then the entry point and context_id parameters are ignored, because all
state is retained for a standby state.

OK, I will update this accordingly.

I think Mark Rutland commented that KVM should define at last interrupts
to the CPU as a wakeup event.

How about using kvm_vcpu_block(vcpu) instead of "vcpu->arch.pause = true"?

This will make CPU_SUSPEND emulation very similar to WFI emulation.

Regards,
Anup

quoted

+
+     return KVM_PSCI_RET_SUCCESS;
+}
+
 static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
 {
      vcpu->arch.pause = true;

@@ -195,6 +211,10 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
               */
              val = 2;
              break;
+     case KVM_PSCI_0_2_FN_CPU_SUSPEND:
+     case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
+             val = kvm_psci_vcpu_suspend(vcpu);
+             break;
      case KVM_PSCI_0_2_FN_CPU_OFF:
              kvm_psci_vcpu_off(vcpu);
              val = KVM_PSCI_RET_SUCCESS;

@@ -232,10 +252,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
              val = KVM_PSCI_RET_SUCCESS;
              ret = 0;
              break;
-     case KVM_PSCI_0_2_FN_CPU_SUSPEND:
-     case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
-             val = KVM_PSCI_RET_NI;
-             break;
      default:
              return -EINVAL;
      }
--

1.7.9.5

Thanks,
-Christoffer