Re: [Xen-devel] [PATCH v2 07/12] x86/IRQ: fix locking around vector management

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, May 13, 2019 at 08:19:04AM -0600, Jan Beulich wrote:
> >>> On 13.05.19 at 15:48, <roger.pau@xxxxxxxxxx> wrote:
> > On Wed, May 08, 2019 at 07:10:59AM -0600, Jan Beulich wrote:
> >> --- a/xen/drivers/passthrough/vtd/iommu.c
> >> +++ b/xen/drivers/passthrough/vtd/iommu.c
> >> @@ -2134,11 +2134,16 @@ static void adjust_irq_affinity(struct a
> >>      unsigned int node = rhsa ? pxm_to_node(rhsa->proximity_domain)
> >>                               : NUMA_NO_NODE;
> >>      const cpumask_t *cpumask = &cpu_online_map;
> >> +    struct irq_desc *desc;
> >>  
> >>      if ( node < MAX_NUMNODES && node_online(node) &&
> >>           cpumask_intersects(&node_to_cpumask(node), cpumask) )
> >>          cpumask = &node_to_cpumask(node);
> >> -    dma_msi_set_affinity(irq_to_desc(drhd->iommu->msi.irq), cpumask);
> >> +
> >> +    desc = irq_to_desc(drhd->iommu->msi.irq);
> >> +    spin_lock_irq(&desc->lock);
> > 
> > I would use the irqsave/irqrestore variants here for extra safety.
> 
> Hmm, maybe. But I think we're in bigger trouble if IRQs indeed
> ended up enabled at any of the two points where this function
> gets called.

I think I'm misreading the above, but if you expect
adjust_irq_affinity to always be called with interrupts disabled using
spin_unlock_irq is wrong as it unconditionally enables interrupts.

Roger.

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