Re: [PATCH v3 06/10] KVM: arm/arm64: use vcpu requests for power_off

Christoffer Dall
2017-05-06T18:17:12Z

On Wed, May 03, 2017 at 06:06:31PM +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,
> closing the race window and also allowing us to remove the final
> check of power_off in VCPU RUN, as the final check for requests
> is sufficient.
>
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
> arch/arm/kvm/arm.c | 3 +--
> arch/arm/kvm/psci.c | 5 ++---
> 2 files changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 7be0d9b0c63a..26d9d4d72853 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -670,8 +670,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> smp_store_mb(vcpu->mode, IN_GUEST_MODE);
>
> if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
> - kvm_request_pending(vcpu) ||
> - vcpu->arch.power_off) {
> + kvm_request_pending(vcpu)) {
> vcpu->mode = OUTSIDE_GUEST_MODE;
> local_irq_enable();
> kvm_pmu_sync_hwstate(vcpu);
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index f68be2cc6256..f189d0ad30d5 100644
> --- a/arch/arm/kvm/psci.c
> +++ b/arch/arm/kvm/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
>

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