linux-kernel - Re: [PATCH v2] iommu: revisit iommu_insert_resv

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Date:   Wed, 21 Aug 2019 14:14:14 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     eric.auger.pro@...il.com, joro@...tes.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        dwmw2@...radead.org, shameerali.kolothum.thodi@...wei.com,
        alex.williamson@...hat.com, robin.murphy@....com
Subject: Re: [PATCH v2] iommu: revisit iommu_insert_resv_region()
 implementation

Hi Christoph,

On 8/6/19 9:32 AM, Christoph Hellwig wrote:
> A couple nitpicks below:
> 
> On Thu, Aug 01, 2019 at 05:59:46PM +0200, Eric Auger wrote:
>> - * The new element is sorted by address with respect to the other
>> - * regions of the same type. In case it overlaps with another
>> - * region of the same type, regions are merged. In case it
>> - * overlaps with another region of different type, regions are
>> - * not merged.
>> + * Elements are sorted by start address and overlapping segments
>> + * of the same type are merged.
>>   */
>> +int iommu_insert_resv_region(struct iommu_resv_region *new,
>> +			     struct list_head *regions)
>>  {
>> +	struct iommu_resv_region *iter, *tmp, *nr, *top;
>> +	struct list_head stack;
>> +	bool added = false;
>>  
>> +	INIT_LIST_HEAD(&stack);

Please forgive me for the delay. I am just back to the office.
> 
> Nit: you could just use
> 
> 	LIST_HEAD(&stack);
> 
> to declare and initialize the variable in a single line.
done
> 
>> +	nr = iommu_alloc_resv_region(new->start, new->length,
>> +				     new->prot, new->type);
>> +	if (!nr)
>>  		return -ENOMEM;
>>  
>> +	/* First add the new elt based on start address sorting */
> 
> /elt/element/ ?
yes
> 
>> +	list_for_each_entry(iter, regions, list) {
>> +		if (nr->start < iter->start) {
>> +			list_add_tail(&nr->list, &iter->list);
>> +			added = true;
>> +			break;
>> +		} else if (nr->start == iter->start && nr->type <= iter->type) {
>> +			list_add_tail(&nr->list, &iter->list);
>> +			added = true;
>> +			break;
>> +		}
> 
> Nit:  no need for an else after a a break.  But then again  both
> branches look identical, so why don't you just merge them:
> 
> 		if (nr->start < iter->start ||
> 		    (nr->start == iter->start && nr->type <= iter->type)) {
> 			list_add_tail(&nr->list, &iter->list);
> 			added = true;
> 			break;
I merged both
> 
> 	}
> 
>> +	if (!added)
>> +		list_add_tail(&nr->list, regions);
> 
> Probably down to preference, but I'd just use a goto to jump past the
> list_add and save the added variable.
done
> 
>> +	/* Merge overlapping segments of type nr->type, if any */
>> +	list_for_each_entry_safe(iter, tmp, regions, list) {
>> +		phys_addr_t top_end, iter_end = iter->start + iter->length - 1;
>> +		bool found = false;
>> +
>> +		/* no merge needed on elements of different types than @nr */
>> +		if (iter->type != nr->type) {
>> +			list_move_tail(&iter->list, &stack);
>> +			continue;
>> +		}
>> +
>> +		/* look for the last stack element of same type as @iter */
>> +		list_for_each_entry_reverse(top, &stack, list)
>> +			if (top->type == iter->type) {
>> +				found = true;
>> +				break;
>> +			}
>> +		if (!found) {
> 
> Same here.
done
> 
>> +			list_move_tail(&iter->list, &stack);
>> +			continue;
>> +		}
>> +
>> +		top_end = top->start + top->length - 1;
>> +
>> +		if (iter->start > top_end + 1) {
>> +			list_move_tail(&iter->list, &stack);
>> +		} else {
>> +			top->length = max(top_end, iter_end) - top->start + 1;
>> +			list_del(&iter->list);
>> +			kfree(iter);
>> +		}
> 
> I wonder if the body of the outer list_for_each_entry_safe loop would
> be a bit nicer in a helper, but again that is probably just down to
> personal preference.
I skipped that suggestion at the moment.

Hope that looks better in v3.

Thank you for your review!

Best Regards

Eric
>