Re: [PATCH v7 05/10] iommu/dma-reserved-iommu: reserved binding rb-tree and helpers

[Robin Murphy]

On 20/04/16 17:18, Eric Auger wrote:
> Robin,
> On 04/20/2016 03:12 PM, Robin Murphy wrote:
> > On 19/04/16 17:56, Eric Auger wrote:
> > > we will need to track which host physical addresses are mapped to
> > > reserved IOVA. In that prospect we introduce a new RB tree indexed
> > > by physical address. This RB tree only is used for reserved IOVA
> > > bindings.
> > >
> > > It is expected this RB tree will contain very few bindings.
> >
> > Sounds like a good reason in favour of using a list, and thus having
> > rather less code here ;)
>
> OK will move to a simple list.
> > >   Those
> > > generally correspond to single page mapping one MSI frame (GICv2m
> > > frame or ITS GITS_TRANSLATER frame).
> > >
> > > Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> > >
> > > ---
> > > v5 -> v6:
> > > - add comment about @d->reserved_lock to be held
> > >
> > > v3 -> v4:
> > > - that code was formerly in "iommu/arm-smmu: add a reserved binding RB
> > > tree"
> > > ---
> > >    drivers/iommu/dma-reserved-iommu.c | 63
> > > ++++++++++++++++++++++++++++++++++++++
> > >    1 file changed, 63 insertions(+)
> > >
> > > diff --git a/drivers/iommu/dma-reserved-iommu.c
> > > b/drivers/iommu/dma-reserved-iommu.c
> > > index 2562af0..f6fa18e 100644
> > > --- a/drivers/iommu/dma-reserved-iommu.c
> > > +++ b/drivers/iommu/dma-reserved-iommu.c
> > > @@ -23,6 +23,69 @@ struct reserved_iova_domain {
> > >        int prot; /* iommu protection attributes to be obeyed */
> > >    };
> > >
> > > +struct iommu_reserved_binding {
> > > +    struct kref        kref;
> > > +    struct rb_node        node;
> > > +    struct iommu_domain    *domain;
> >
> > Hang on, the tree these are in is already embedded in a domain. Ergo we
> > can't look them up without first knowing the domain they belong to, so
> > what purpose does this guy serve?
> this is used on the kref_put. The release function takes a kref; then we
> get the container to retrieve the binding and storing the domain here
> enables to unlink the node.

Ah yes, I see now - that's annoyingly awkward. I think it could possibly 
be avoided in the list case (if the kref_put callback just did 
list_del_init(), the entry could then be checked for an empty list and 
disposed of outside the lock), but I'm not sure whether that's really 
worth the fuss. Oh well.

Robin.

> Best Regards
>
> Eric
> > Robin.
> >
> > > +    phys_addr_t        addr;
> > > +    dma_addr_t        iova;
> > > +    size_t            size;
> > > +};
> > > +
> > > +/* Reserved binding RB-tree manipulation */
> > > +
> > > +/* @d->reserved_lock must be held */
> > > +static struct iommu_reserved_binding *find_reserved_binding(
> > > +                    struct iommu_domain *d,
> > > +                    phys_addr_t start, size_t size)
> > > +{
> > > +    struct rb_node *node = d->reserved_binding_list.rb_node;
> > > +
> > > +    while (node) {
> > > +        struct iommu_reserved_binding *binding =
> > > +            rb_entry(node, struct iommu_reserved_binding, node);
> > > +
> > > +        if (start + size <= binding->addr)
> > > +            node = node->rb_left;
> > > +        else if (start >= binding->addr + binding->size)
> > > +            node = node->rb_right;
> > > +        else
> > > +            return binding;
> > > +    }
> > > +
> > > +    return NULL;
> > > +}
> > > +
> > > +/* @d->reserved_lock must be held */
> > > +static void link_reserved_binding(struct iommu_domain *d,
> > > +                  struct iommu_reserved_binding *new)
> > > +{
> > > +    struct rb_node **link = &d->reserved_binding_list.rb_node;
> > > +    struct rb_node *parent = NULL;
> > > +    struct iommu_reserved_binding *binding;
> > > +
> > > +    while (*link) {
> > > +        parent = *link;
> > > +        binding = rb_entry(parent, struct iommu_reserved_binding,
> > > +                   node);
> > > +
> > > +        if (new->addr + new->size <= binding->addr)
> > > +            link = &(*link)->rb_left;
> > > +        else
> > > +            link = &(*link)->rb_right;
> > > +    }
> > > +
> > > +    rb_link_node(&new->node, parent, link);
> > > +    rb_insert_color(&new->node, &d->reserved_binding_list);
> > > +}
> > > +
> > > +/* @d->reserved_lock must be held */
> > > +static void unlink_reserved_binding(struct iommu_domain *d,
> > > +                    struct iommu_reserved_binding *old)
> > > +{
> > > +    rb_erase(&old->node, &d->reserved_binding_list);
> > > +}
> > > +
> > >    int iommu_alloc_reserved_iova_domain(struct iommu_domain *domain,
> > >                         dma_addr_t iova, size_t size, int prot,
> > >                         unsigned long order)