Re: [Xen-devel] [PATCH for 4.5] x86/VPMU: Clear last_vcpu when destroying VPMU

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.12.14 at 22:20, <boris.ostrovsky@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vpmu.c
> +++ b/xen/arch/x86/hvm/vpmu.c
> @@ -247,10 +247,32 @@ void vpmu_initialise(struct vcpu *v)
>      }
>  }
>  
> +static void vpmu_clear_last(void *arg)
> +{
> +    struct vcpu *v = (struct vcpu *)arg;

Please drop this pointless cast, or perhaps the entire variable, as ...

> +
> +    if ( this_cpu(last_vcpu) == v )

... you don't really need it to be of "struct vcpu *" type - "void *"
is quite fine for a comparison.

> +        this_cpu(last_vcpu) = NULL;
> +}
> +
>  void vpmu_destroy(struct vcpu *v)
>  {
>      struct vpmu_struct *vpmu = vcpu_vpmu(v);
>  
> +    if ( vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
> +    {
> +        /* Need to clear last_vcpu in case it points to v */
> +        if ( vpmu->last_pcpu != smp_processor_id() )
> +            on_selected_cpus(cpumask_of(vpmu->last_pcpu),
> +                             vpmu_clear_last, (void *)v, 1);

The cast here is pointless too. But considering your subsequent
reply this code may go away altogether anyway; if it doesn't,
explaining (in the commit message) why you need to use an IPI
here would seem necessary.

> +        else
> +        {
> +            local_irq_disable();
> +            vpmu_clear_last((void *)v);

And another pointless cast.

Jan


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