Re: [PATCH] iommu/iova: Separate out rcache init

[John Garry]

Hi Robin,

> > Signed-off-by: John Garry<john.garry@xxxxxxxxxx>
> Mangled patch? (no "---" separator here)

hmm... not sure. As an experiment, I just downloaded this patch from 
lore.kernel.org and it applies ok.

> Overall this looks great, just a few comments further down...

...

> > +}
> > +EXPORT_SYMBOL_GPL(iova_domain_init_rcaches);
> > +
> > +void iova_domain_free_rcaches(struct iova_domain *iovad)
> > +{
> > +	cpuhp_state_remove_instance_nocalls(CPUHP_IOMMU_IOVA_DEAD,
> > +					    &iovad->cpuhp_dead);
> > +	free_iova_rcaches(iovad);
> >    }
> > +EXPORT_SYMBOL_GPL(iova_domain_free_rcaches);
> I think we should continue to expect external callers to clean up with
> put_iova_domain(). 

ok, fine, makes sense

> If they aren't doing that already they have a bug
> (albeit minor), and we don't want to give the impression that it's OK to
> free the caches at any point*other*  than tearing down the whole
> iova_domain, since the implementation really wouldn't expect that.
>
> >    /*
> >     * Try inserting IOVA range starting with 'iova_pfn' into 'rcache', and
> > @@ -831,7 +872,7 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
> >    {
> >    	unsigned int log_size = order_base_2(size);
> >    
> > -	if (log_size >= IOVA_RANGE_CACHE_MAX_SIZE)
> > +	if (log_size >= IOVA_RANGE_CACHE_MAX_SIZE || !iovad->rcaches)
> >    		return 0;
> >    

..

> > @@ -102,6 +92,8 @@ struct iova *reserve_iova(struct iova_domain *iovad, unsigned long pfn_lo,
> >    	unsigned long pfn_hi);
> >    void init_iova_domain(struct iova_domain *iovad, unsigned long granule,
> >    	unsigned long start_pfn);
> > +int iova_domain_init_rcaches(struct iova_domain *iovad);
> > +void iova_domain_free_rcaches(struct iova_domain *iovad);
> As above, I vote for just forward-declaring the free routine in iova.c
> and keeping it entirely private.

ok

> >    struct iova *find_iova(struct iova_domain *iovad, unsigned long pfn);
> >    void put_iova_domain(struct iova_domain *iovad);
> >    #else
> > @@ -157,6 +149,15 @@ static inline void init_iova_domain(struct iova_domain *iovad,
> >    {
> >    }
> >    
> > +static inline int iova_domain_init_rcaches(struct iova_domain *iovad)
> > +{
> > +	return -ENOTSUPP;
> > +}
> > +
> > +static inline void iova_domain_free_rcaches(struct iova_domain *iovad)
> > +{
> > +}
> > +
> I'd be inclined not to add stubs at all - I think it's a reasonable
> assumption that anyone involved enough to care about rcaches has a hard
> dependency on IOMMU_IOVA already.

So iova_domain_free_rcaches() would disappear from here as a result of 
the changes discussed above.

As for iova_domain_init_rcaches(), I was just following the IOMMU/IOVA 
coding practice - that is, always stub.

> It's certainly the case today, and I'd
> hardly want to encourage more users anyway.

I think that stronger deterrents would be needed :)

Anyway, I can remove it.

Thanks,
John