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

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Message-ID: <571A2186.1050004@arm.com>
Date:	Fri, 22 Apr 2016 14:05:10 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Eric Auger <eric.auger@...aro.org>, eric.auger@...com,
	alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org,
	tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com,
	christoffer.dall@...aro.org, linux-arm-kernel@...ts.infradead.org
Cc:	patches@...aro.org, linux-kernel@...r.kernel.org,
	Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com,
	p.fedin@...sung.com, iommu@...ts.linux-foundation.org,
	Jean-Philippe.Brucker@....com, julien.grall@....com
Subject: Re: [PATCH v7 05/10] iommu/dma-reserved-iommu: reserved binding
 rb-tree and helpers

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@...aro.org>
>>>
>>> ---
>>> 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)
>>>
>>
>