Re: [PATCH v2 28/45] KVM: Use get/put_online_cpus_atomic() to prevent CPU offline

[Paolo Bonzini <pbonzini@redhat.com>]

Il 25/06/2013 22:30, Srivatsa S. Bhat ha scritto:
> Once stop_machine() is gone from the CPU offline path, we won't be able
> to depend on disabling preemption to prevent CPUs from going offline
> from under us.
> 
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
> offline, while invoking from atomic context.
> 
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: kvm@vger.kernel.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---
> 
>  virt/kvm/kvm_main.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 302681c..5bbfa30 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -174,7 +174,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
>  
>  	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
>  
> -	me = get_cpu();
> +	me = get_online_cpus_atomic();
>  	kvm_for_each_vcpu(i, vcpu, kvm) {
>  		kvm_make_request(req, vcpu);
>  		cpu = vcpu->cpu;
> @@ -192,7 +192,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
>  		smp_call_function_many(cpus, ack_flush, NULL, 1);
>  	else
>  		called = false;
> -	put_cpu();
> +	put_online_cpus_atomic();
>  	free_cpumask_var(cpus);
>  	return called;
>  }
> @@ -1707,11 +1707,11 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
>  		++vcpu->stat.halt_wakeup;
>  	}
>  
> -	me = get_cpu();
> +	me = get_online_cpus_atomic();
>  	if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
>  		if (kvm_arch_vcpu_should_kick(vcpu))
>  			smp_send_reschedule(cpu);
> -	put_cpu();
> +	put_online_cpus_atomic();
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_kick);
>  #endif /* !CONFIG_S390 */
> 
> --
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> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>