Re: [PATCH 3/7] iommu/iova: insert start_pfn boundary of dma32

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

Because the problem of my email-server, all patches sent to Joerg Roedel <joro@8bytes.org> failed.
So I repost this email again.


On 2017/3/24 11:43, Leizhen (ThunderTown) wrote:
> 
> 
> On 2017/3/23 21:01, Robin Murphy wrote:
>> On 22/03/17 06:27, Zhen Lei wrote:
>>> Reserve the first granule size memory(start at start_pfn) as boundary
>>> iova, to make sure that iovad->cached32_node can not be NULL in future.
>>> Meanwhile, changed the assignment of iovad->cached32_node from rb_next to
>>> rb_prev of &free->node in function __cached_rbnode_delete_update.
>>
>> I'm not sure I follow this. It's a top-down allocator, so cached32_node
>> points to the last node allocated (or the node above the last one freed)
>> on the assumption that there is likely free space directly below there,
>> thus it's a pretty good place for the next allocation to start searching
>> from. On the other hand, start_pfn is a hard "do not go below this line"
>> limit, so it doesn't seem to make any sense to ever point the former at
>> the latter.
> This patch just prepares for dma64. Because we really need to add the boundary
> between dma32 and dma64, there are two main purposes:
> 1. to make dma32 iova allocation faster, because the last node which dma32 can be
> seen is the boundary. So dma32 iova allocation will only try within dma32 iova space.
> Meanwhile, we hope dma64 allocation try dma64 iova space(iova>=4G) first, because the
> maxium dma32 iova space is 4GB, dma64 iova space is almost richer than dma32.
> 
> 2. to prevent a allocated iova cross dma32 and dma64 space. Otherwise, this special
> case should be considered when allocate and free iova.
> 
> After the above boundary added, it's better to add start_pfn of dma32 boundary also,
> to make them to be considered in one model.
> 
> After the two boundaries added, adjust cached32/64_node point to the free iova node can
> simplified programming.
> 
> 
>>
>> I could understand slightly more if we were reserving the PFN *above*
>> the cached range, but as-is I don't see what we gain from the change
>> here, nor what benefit the cached32_node != NULL assumption gives
>> (AFAICS it would be more useful to simply restrict the cases where it
>> may be NULL to when the address space is either completely full or
>> completely empty, or perhaps both).
>>
>> Robin.
>>
>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>> ---
>>>  drivers/iommu/iova.c | 63 ++++++++++++++++++++++++++++++----------------------
>>>  1 file changed, 37 insertions(+), 26 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
>>> index 1c49969..b5a148e 100644
>>> --- a/drivers/iommu/iova.c
>>> +++ b/drivers/iommu/iova.c
>>> @@ -32,6 +32,17 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
>>>  static void init_iova_rcaches(struct iova_domain *iovad);
>>>  static void free_iova_rcaches(struct iova_domain *iovad);
>>>  
>>> +static void
>>> +insert_iova_boundary(struct iova_domain *iovad)
>>> +{
>>> +	struct iova *iova;
>>> +	unsigned long start_pfn_32bit = iovad->start_pfn;
>>> +
>>> +	iova = reserve_iova(iovad, start_pfn_32bit, start_pfn_32bit);
>>> +	BUG_ON(!iova);
>>> +	iovad->cached32_node = &iova->node;
>>> +}
>>> +
>>>  void
>>>  init_iova_domain(struct iova_domain *iovad, unsigned long granule,
>>>  	unsigned long start_pfn, unsigned long pfn_32bit)
>>> @@ -45,27 +56,38 @@ init_iova_domain(struct iova_domain *iovad, unsigned long granule,
>>>  
>>>  	spin_lock_init(&iovad->iova_rbtree_lock);
>>>  	iovad->rbroot = RB_ROOT;
>>> -	iovad->cached32_node = NULL;
>>>  	iovad->granule = granule;
>>>  	iovad->start_pfn = start_pfn;
>>>  	iovad->dma_32bit_pfn = pfn_32bit;
>>>  	init_iova_rcaches(iovad);
>>> +
>>> +	/*
>>> +	 * Insert boundary nodes for dma32. So cached32_node can not be NULL in
>>> +	 * future.
>>> +	 */
>>> +	insert_iova_boundary(iovad);
>>>  }
>>>  EXPORT_SYMBOL_GPL(init_iova_domain);
>>>  
>>>  static struct rb_node *
>>>  __get_cached_rbnode(struct iova_domain *iovad, unsigned long *limit_pfn)
>>>  {
>>> -	if ((*limit_pfn > iovad->dma_32bit_pfn) ||
>>> -		(iovad->cached32_node == NULL))
>>> +	struct rb_node *cached_node;
>>> +	struct rb_node *next_node;
>>> +
>>> +	if (*limit_pfn > iovad->dma_32bit_pfn)
>>>  		return rb_last(&iovad->rbroot);
>>> -	else {
>>> -		struct rb_node *prev_node = rb_prev(iovad->cached32_node);
>>> -		struct iova *curr_iova =
>>> -			rb_entry(iovad->cached32_node, struct iova, node);
>>> -		*limit_pfn = curr_iova->pfn_lo - 1;
>>> -		return prev_node;
>>> +	else
>>> +		cached_node = iovad->cached32_node;
>>> +
>>> +	next_node = rb_next(cached_node);
>>> +	if (next_node) {
>>> +		struct iova *next_iova = rb_entry(next_node, struct iova, node);
>>> +
>>> +		*limit_pfn = min(*limit_pfn, next_iova->pfn_lo - 1);
>>>  	}
>>> +
>>> +	return cached_node;
>>>  }
>>>  
>>>  static void
>>> @@ -83,20 +105,13 @@ __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free)
>>>  	struct iova *cached_iova;
>>>  	struct rb_node *curr;
>>>  
>>> -	if (!iovad->cached32_node)
>>> -		return;
>>>  	curr = iovad->cached32_node;
>>>  	cached_iova = rb_entry(curr, struct iova, node);
>>>  
>>>  	if (free->pfn_lo >= cached_iova->pfn_lo) {
>>> -		struct rb_node *node = rb_next(&free->node);
>>> -		struct iova *iova = rb_entry(node, struct iova, node);
>>> -
>>>  		/* only cache if it's below 32bit pfn */
>>> -		if (node && iova->pfn_lo < iovad->dma_32bit_pfn)
>>> -			iovad->cached32_node = node;
>>> -		else
>>> -			iovad->cached32_node = NULL;
>>> +		if (free->pfn_hi <= iovad->dma_32bit_pfn)
>>> +			iovad->cached32_node = rb_prev(&free->node);
>>>  	}
>>>  }
>>>  
>>> @@ -114,7 +129,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
>>>  		unsigned long size, unsigned long limit_pfn,
>>>  			struct iova *new, bool size_aligned)
>>>  {
>>> -	struct rb_node *prev, *curr = NULL;
>>> +	struct rb_node *prev, *curr;
>>>  	unsigned long flags;
>>>  	unsigned long saved_pfn;
>>>  	unsigned long pad_size = 0;
>>> @@ -144,13 +159,9 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
>>>  		curr = rb_prev(curr);
>>>  	}
>>>  
>>> -	if (!curr) {
>>> -		if (size_aligned)
>>> -			pad_size = iova_get_pad_size(size, limit_pfn);
>>> -		if ((iovad->start_pfn + size + pad_size) > limit_pfn) {
>>> -			spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
>>> -			return -ENOMEM;
>>> -		}
>>> +	if (unlikely(!curr)) {
>>> +		spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
>>> +		return -ENOMEM;
>>>  	}
>>>  
>>>  	/* pfn_lo will point to size aligned address if size_aligned is set */
>>>
>>
>>
>> .
>>
> 

-- 
Thanks!
BestRegards