Re: [PATCH v4 06/11] KVM: arm/arm64: use vcpu requests for power_off

Christoffer Dall
2017-06-01T10:35:17Z

On Tue, May 16, 2017 at 04:20:30AM +0200, Andrew Jones wrote:
> System shutdown is currently using request-less VCPU kicks. This
> leaves open a tiny race window, as it doesn't ensure the state
> change to power_off is seen by a VCPU just about to enter guest
> mode. VCPU requests, OTOH, are guaranteed to be seen (see "Ensuring
> Requests Are Seen" of Documentation/virtual/kvm/vcpu-requests.rst)
> This patch applies the EXIT request used by pause to power_off,
> fixing the race.
>
> Signed-off-by: Andrew Jones <drjones@redhat.com>

Reviewed-by: Christoffer Dall <cdall@linaro.org>

> ---
> virt/kvm/arm/psci.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
> index f68be2cc6256..f189d0ad30d5 100644
> --- a/virt/kvm/arm/psci.c
> +++ b/virt/kvm/arm/psci.c
> @@ -179,10 +179,9 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
> * after this call is handled and before the VCPUs have been
> * re-initialized.
> */
> - kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> + kvm_for_each_vcpu(i, tmp, vcpu->kvm)
> tmp->arch.power_off = true;
> - kvm_vcpu_kick(tmp);
> - }
> + kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_VCPU_EXIT);
>
> memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event));
> vcpu->run->system_event.type = type;
> --
> 2.9.3
>