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

[Christoffer Dall <cdall@linaro.org>]

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
>