Re: [Xen-devel] [PATCH v6 2/5] xen/arm: inflight irqs during migration

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 27 Jun 2014, Ian Campbell wrote:
> On Mon, 2014-06-23 at 17:37 +0100, Stefano Stabellini wrote:
> > - replace the dsb with smb_wmb and smb_rmb, use them to ensure the order
> > of accesses to GIC_IRQ_GUEST_QUEUED and GIC_IRQ_GUEST_MIGRATING.
> 
> You access/change those with test_bit et al which already include
> appropriate barriers/ordering guarantees, I think.
> 
> The __test_foo are the variants without ordering.
> 
> IOW I think you can probably do without some/all of those barriers.
> 
> > @@ -546,6 +575,8 @@ static int vgic_distr_mmio_write(struct vcpu *v, 
> > mmio_info_t *info)
> >      int offset = (int)(info->gpa - v->domain->arch.vgic.dbase);
> >      int gicd_reg = REG(offset);
> >      uint32_t tr;
> > +    unsigned long trl;
> 
> Can you add /* Need unsigned long for XXX */?
> 
> Actually, even better would be to call this variable "target" or
> something. (tgt?)
> 
> And even better than that would be:
> 
>  case GICD_ITARGETSR + 8 ... GICD_ITARGETSRN:
>  {
>       unsigned long target;
>       ... stuff ...
>       return 1;
>  }

OK

> so the scope is limited to the uses.
> 
> > +    int i;
> >  
> >      switch ( gicd_reg )
> >      {
> [...]
> > @@ -786,9 +837,14 @@ void vgic_vcpu_inject_irq(struct vcpu *v, unsigned int 
> > irq)
> >  
> >      spin_lock_irqsave(&v->arch.vgic.lock, flags);
> >  
> > +    set_bit(GIC_IRQ_GUEST_QUEUED, &n->status);
> > +    /* update QUEUED before MIGRATING */
>                                ^testing
> 
> (otherwise I wonder why you aren't setting it)

right

> > +    smp_wmb();
> > +    if ( test_bit(GIC_IRQ_GUEST_MIGRATING, &n->status) )
> > +        goto out;
> > +
> >      if ( !list_empty(&n->inflight) )
> >      {
> > -        set_bit(GIC_IRQ_GUEST_QUEUED, &n->status);
> >          gic_raise_inflight_irq(v, irq);
> >          goto out;
> >      }
> 
> Ian.
> 
> 

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