Re: [Xen-devel] [PATCH 3/3] VMX: Remove the vcpu from the per-cpu blocking list after domain termination

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Dario Faggioli [mailto:dario.faggioli@xxxxxxxxxx]
> Sent: Monday, May 23, 2016 8:31 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>; xen-devel@xxxxxxxxxxxxx
> Cc: keir@xxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; jbeulich@xxxxxxxx;
> andrew.cooper3@xxxxxxxxxx; george.dunlap@xxxxxxxxxxxxx;
> konrad.wilk@xxxxxxxxxx
> Subject: Re: [PATCH 3/3] VMX: Remove the vcpu from the per-cpu blocking list
> after domain termination
> 
> On Fri, 2016-05-20 at 16:53 +0800, Feng Wu wrote:
> > We need to make sure the bocking vcpu is not in any per-cpu blocking
> > list
> > when the associated domain is going to be destroyed.
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > ---
> >
> > --- a/xen/arch/x86/hvm/vmx/vmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vmx.c
> > @@ -248,6 +248,36 @@ void vmx_pi_hooks_deassign(struct domain *d)
> >      d->arch.hvm_domain.vmx.pi_switch_to = NULL;
> >  }
> >
> > +static void vmx_pi_blocking_list_cleanup(struct domain *d)
> > +{
> > +    unsigned int cpu;
> > +
> > +    for_each_online_cpu ( cpu )
> > +    {
> > +        struct vcpu *v;
> > +        unsigned long flags;
> > +        struct arch_vmx_struct *vmx, *tmp;
> > +        spinlock_t *lock = &per_cpu(vmx_pi_blocking, cpu).lock;
> > +        struct list_head *blocked_vcpus = &per_cpu(vmx_pi_blocking,
> > cpu).list;
> > +
> > +        spin_lock_irqsave(lock, flags);
> > +
> > +        list_for_each_entry_safe(vmx, tmp, blocked_vcpus,
> > pi_blocking.list)
> > +        {
> > +            v = container_of(vmx, struct vcpu, arch.hvm_vmx);
> > +
> > +            if (v->domain == d)
> > +            {
> > +                list_del(&vmx->pi_blocking.list);
> > +                ASSERT(vmx->pi_blocking.lock == lock);
> > +                vmx->pi_blocking.lock = NULL;
> > +            }
> > +        }
> > +
> > +        spin_unlock_irqrestore(lock, flags);
> > +    }
> >
> So, I'm probably missing something very ver basic, but I don't see
> what's the reason why we need this loop... can't we arrange for
> checking
> 
>  list_empty(&v->arch.hvm_vmx.pi_blocking.list)

Yes, I also cannot find the reason why can't we use this good
suggestion, Except we need use list_del_init() instead of
list_del() in the current code. Or we can just check whether
' vmx->pi_blocking.lock ' is NULL? I total don't know why I
missed it! :)

Thanks,
Feng

> 
> ?
> 
> :-O
> 
> Regards,
> Dario
> --
> <<This happens because I choose it to happen!>> (Raistlin Majere)
> -----------------------------------------------------------------
> Dario Faggioli, Ph.D, http://about.me/dario.faggioli
> Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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