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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/13/2014 02:08 PM, Konrad Rzeszutek Wilk wrote:
> 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@xxxxxxxxxx>
> Release-Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
I would like to send a slightly better patch on Monday (along the same 
lines but trying to avoid unnecessary IPIs if not needed).
-boris


> > ---
> >   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

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