Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier

[Yan Zhao <yan.y.zhao@intel.com>]

On Sat, Jun 27, 2020 at 08:57:14AM -0400, Peter Xu wrote:
> On Sat, Jun 27, 2020 at 03:26:45AM -0400, Yan Zhao wrote:
> > > -    assert(entry->iova >= notifier->start && entry_end <= notifier->end);
> > > +    if (notifier->notifier_flags & IOMMU_NOTIFIER_ARBITRARY_MASK) {
> > > +        tmp.iova = MAX(tmp.iova, notifier->start);
> > > +        tmp.addr_mask = MIN(tmp.addr_mask, notifier->end);
> > NIT:
> >        tmp.addr_mask = MIN(entry_end, notifier->end) - tmp.iova;
> 
> Right.  Thanks. :)
> 
> > > +        assert(tmp.iova <= tmp.addr_mask);
> > no this assertion then.
> 
> Or change it into:
> 
>   assert(MIN(entry_end, notifier->end) >= tmp.iova);
> 
> To double confirm no overflow.
>
what about assert in this way, so that it's also useful to check overflow
in the other condition.

hwaddr entry_end = entry->iova + entry->addr_mask;
+
+ assert(notifier->end >= notifer->start && entry_end >= entry->iova);


then as there's a following filter
    if (notifier->start > entry_end || notifier->end < entry->iova) {
        return;
    }

we can conclude that

entry_end >= entry->iova(tmp.iova)
entry_end >= notifier->start,
--> entry_end >= MAX(tmp.iova, notfier->start)
--> entry_end >= tmp.iova


notifier->end >= entry->iova (tmp.iova),
notifier->end >= notifer->start,
--> notifier->end >= MAX(tmp.iova, nofier->start)
--> notifier->end >= tmp.iova

==> MIN(end_end, notifer->end) >= tmp.iova

Thanks
Yan