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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Dec 12, 2014 at 04:20:48PM -0500, Boris Ostrovsky wrote:
> We need to make sure that last_vcpu is not pointing to VCPU whose
> VPMU is being destroyed. Otherwise we may try dereference it in
> the future, when VCPU is gone.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Release-Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
>  xen/arch/x86/hvm/vpmu.c |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
> 
> This needs to be backported to 4.3 and 4.4 as well
> 
> diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
> index 1df74c2..6d39680 100644
> --- 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;
> +
> +    if ( this_cpu(last_vcpu) == v )
> +        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);
> +        else
> +        {
> +            local_irq_disable();
> +            vpmu_clear_last((void *)v);
> +            local_irq_enable();
> +        }
> +    }
> +
>      if ( vpmu->arch_vpmu_ops && vpmu->arch_vpmu_ops->arch_vpmu_destroy )
>          vpmu->arch_vpmu_ops->arch_vpmu_destroy(v);
>  }
> -- 
> 1.7.1
>