Re: [Xen-devel] [PATCH v9 04/12] xen/arm: support HW interrupts, do not request maintenance_interrupts

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 11 Jun 2014, Julien Grall wrote:
> Hi Stefano,
> 
> On 06/10/2014 03:07 PM, Stefano Stabellini wrote:
> > +static void gic_update_one_lr(struct vcpu *v, int i)
> > +{
> > +    struct pending_irq *p;
> > +    uint32_t lr;
> > +    int irq;
> > +
> > +    ASSERT(spin_is_locked(&v->arch.vgic.lock));
> > +
> > +    lr = GICH[GICH_LR + i];
> > +    if ( !(lr & (GICH_LR_PENDING|GICH_LR_ACTIVE)) )
> > +    {
> > +        GICH[GICH_LR + i] = 0;
> > +        clear_bit(i, &this_cpu(lr_mask));
> > +
> > +        irq = (lr >> GICH_LR_VIRTUAL_SHIFT) & GICH_LR_VIRTUAL_MASK;
> > +        p = irq_to_pending(v, irq);
> > +        if ( p->desc != NULL )
> > +            p->desc->status &= ~IRQ_INPROGRESS;
> 
> Reading again this patch... shouldn't we take the desc->lock here?
> 
> It's possible to receive the same interrupt while we update the LRs
> (depending how the IRQ has been physically route) so we may overwrite
> the IRQ_INPROGRESS bit.

It is not possible, because we have interrupts disabled at this point.
A later patch introduce

ASSERT(!local_irq_is_enabled());

at the beginning of gic_update_one_lr.

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