On 2013-12-18 06:26, Christoffer Dall wrote:

The current KVM implementation of PSCI returns INVALID_PARAMETERS if the waitqueue for the corresponding CPU is not active. This does not seem correct, since KVM should not care what the specific thread is doing, for example, user space may not have called KVM_RUN on this VCPU yet or the thread may be busy looping to user space because it received a signal; this is really up to the user space implementation. Instead we should check specifically that the CPU is marked as being turned off, regardless of the VCPU thread state, and if it is, we shall simply clear the pause flag on the CPU and wake up the thread if it happens to be blocked for us.

Further, the implementation seems to be racy when executing multiple VCPU threads. There really isn't a reasonable user space programming scheme to ensure all secondary CPUs have reached kvm_vcpu_first_run_init before turning on the boot CPU.

Therefore, set the pause flag on the vcpu at VCPU init time (which can reasonably be expected to be completed for all CPUs by user space before running any VCPUs) and clear both this flag and the feature (in case the feature can somehow get set again in the future) and ping the waitqueue on turning on a VCPU using PSCI.

Reported-by: Peter Maydell peter.maydell@linaro.org Signed-off-by: Christoffer Dall christoffer.dall@linaro.org

Acked-by: Marc Zyngier marc.zyngier@arm.com

---

Changes[v2]:

• Use non-atomic version of test_and_clear_bit instead
• Check if vcpu is paused and return KVM_PSCI_RET_INVAL if not
• Remove unnecessary feature bit clear

arch/arm/kvm/arm.c | 30 +++++++++++++++++++----------- arch/arm/kvm/psci.c | 11 ++++++----- 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c index 2a700e0..151eb91 100644 --- a/arch/arm/kvm/arm.c +++ b/arch/arm/kvm/arm.c @@ -478,15 +478,6 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) return ret; }

• /*

• * Handle the "start in power-off" case by calling into the
  

• * PSCI code.
  

• */
  

• if (test_and_clear_bit(KVM_ARM_VCPU_POWER_OFF,

vcpu->arch.features)) {

• *vcpu_reg(vcpu, 0) = KVM_PSCI_FN_CPU_OFF;
  

• kvm_psci_call(vcpu);
  

• }
• return 0;

}

@@ -700,6 +691,24 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, return -EINVAL; }

+static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,

• 			 struct kvm_vcpu_init *init)
  

+{

• int ret;
• ret = kvm_vcpu_set_target(vcpu, init);
• if (ret)

• return ret;
  

• /*

• * Handle the "start in power-off" case by marking the VCPU as 
  

paused.

• */
  

• if (__test_and_clear_bit(KVM_ARM_VCPU_POWER_OFF,

vcpu->arch.features))

• vcpu->arch.pause = true;
  

• return 0;

+}

long kvm_arch_vcpu_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) { @@ -713,8 +722,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp, if (copy_from_user(&init, argp, sizeof(init))) return -EFAULT;

• return kvm_vcpu_set_target(vcpu, &init);
  

• return kvm_arch_vcpu_ioctl_vcpu_init(vcpu, &init);
  

  } case KVM_SET_ONE_REG: case KVM_GET_ONE_REG: {

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c index 0881bf1..448f60e 100644 --- a/arch/arm/kvm/psci.c +++ b/arch/arm/kvm/psci.c @@ -54,15 +54,15 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) } }

• if (!vcpu)

• /*

• * Make sure the caller requested a valid CPU and that the CPU is
  

• * turned off.
  

• */
  

• if (!vcpu || !vcpu->arch.pause) return KVM_PSCI_RET_INVAL;

  target_pc = *vcpu_reg(source_vcpu, 2);

• wq = kvm_arch_vcpu_wq(vcpu);

• if (!waitqueue_active(wq))

• return KVM_PSCI_RET_INVAL;
  

• kvm_reset_vcpu(vcpu);

  /* Gracefully handle Thumb2 entry point */

@@ -79,6 +79,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) vcpu->arch.pause = false; smp_mb(); /* Make sure the above is visible */

• wq = kvm_arch_vcpu_wq(vcpu); wake_up_interruptible(wq);

  return KVM_PSCI_RET_SUCCESS;