Re: [Qemu-devel] [PATCH v4 2/3] memory: introduce IOMMUOps.notify_flag_changed

[David Gibson]

On Wed, Sep 14, 2016 at 03:12:43PM +0800, Peter Xu wrote:
> On Wed, Sep 14, 2016 at 03:55:28PM +1000, David Gibson wrote:
> 
> [...]
> 
> > > -static void vtd_iommu_notify_started(MemoryRegion *iommu)
> > > +static void vtd_iommu_notify_flag_changed(MemoryRegion *iommu,
> > > +                                          IOMMUNotifierFlag old,
> > > +                                          IOMMUNotifierFlag new)
> > >  {
> > >      VTDAddressSpace *vtd_as = container_of(iommu, VTDAddressSpace, 
> > > iommu);
> > 
> > Shouldn't this have a sanity check that the new flags doesn't include
> > MAP actions?
> 
> See your r-b for patch 3, thanks! So skipping this one.
> 
> [...]
> 
> > > +static void spapr_tce_notify_flag_changed(MemoryRegion *iommu,
> > > +                                          IOMMUNotifierFlag old,
> > > +                                          IOMMUNotifierFlag new)
> > > +{
> > > +    if (old == IOMMU_NOTIFIER_NONE && new == IOMMU_NOTIFIER_ALL) {
> > > +        spapr_tce_notify_started(iommu);
> > > +    } else if (old == IOMMU_NOTIFIER_ALL && new == IOMMU_NOTIFIER_NONE) {
> > > +        spapr_tce_notify_stopped(iommu);
> > > +    }
> > 
> > This is wrong.  We need to do the notify_start and stop actions if
> > *any* bits are set in the new/old flags, not just if all of them are
> > set.
> 
> Power should need both, right? I can switch all
> 
>   "== IOMMU_NOTIFIER_ALL"
> 
> into:
> 
>   "!= IOMMU_NOTIFIER_NONE"

Yes, that should be right.

> in the next version if you like, but AFAICT they are totally the
> same.

Again, only if you assume things about how the notifiers will be used,
which is not a good look when designing an interface.

> 
> > 
> > I'd also prefer to see notify_started and notify_stopped folded into
> > this function.
> 
> I can do that for v5.
> 
> Thanks,
> 
> -- peterx
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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