Re: [PATCH] iommu: revisit iommu_insert_resv_region() implementation

[Auger Eric <eric.auger@redhat.com>]

Hi Shameer,

On 8/1/19 3:46 PM, Shameerali Kolothum Thodi wrote:
> Hi Eric,
> 
>> -----Original Message-----
>> From: Eric Auger [mailto:eric.auger@redhat.com]
>> Sent: 30 July 2019 15:01
>> To: eric.auger.pro@gmail.com; eric.auger@redhat.com; joro@8bytes.org;
>> iommu@lists.linux-foundation.org; linux-kernel@vger.kernel.org;
>> dwmw2@infradead.org; alex.williamson@redhat.com;
>> robin.murphy@arm.com; hch@infradead.org
>> Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
>> Subject: [PATCH] iommu: revisit iommu_insert_resv_region() implementation
>>
>> Current implementation is recursive and in case of allocation
>> failure the existing @regions list is altered. A non recursive
>> version looks better for maintainability and simplifies the
>> error handling. We use a separate stack for overlapping segment
>> merging.
>>
>> Note this new implementation may change the region order of
>> appearance in /sys/kernel/iommu_groups/<n>/reserved_regions
>> files but this order has never been documented, see
>> commit bc7d12b91bd3 ("iommu: Implement reserved_regions
>> iommu-group sysfs file"). Previously the regions were sorted
>> by start address. Now they are first sorted by type and within
>> a type they are sorted by start address.
> 
> I had a quick run with this patch on one of our boards(D05) where we
> actually have an untranslated HW MSI region.
> 
> Before..
> estuary:/$ cat /sys/kernel/iommu_groups/3/reserved_regions
> 0x0000000008000000 0x00000000080fffff msi
> 0x00000000c6010000 0x00000000c601ffff msi 
> 
> After...
> estuary:/$ cat /sys/kernel/iommu_groups/3/reserved_regions
> 0x00000000c6010000 0x00000000c601ffff msi
> 0x0000000008000000 0x00000000080fffff msi
> 
> I think the order is reversed now because they are both different types, but are 
> called "msi". Slightly confusing, but not sure it's a good idea to change the
> description to something more obvious. 

Thank you very much for the testing. I have been working on another
version which removes the recursiveness but still sorts by start address
and then by type. I prefer this new one as this shouldn't change the
order. I will submit it asap.

Thanks

Eric
> 
> Cheers,
> Shameer
> 
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>> ---
>>  drivers/iommu/iommu.c | 96 ++++++++++++++++++++++---------------------
>>  1 file changed, 50 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 0c674d80c37f..7479f3d38e61 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -229,60 +229,64 @@ static ssize_t iommu_group_show_name(struct
>> iommu_group *group, char *buf)
>>   * @new: new region to insert
>>   * @regions: list of regions
>>   *
>> - * 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 region type and elements of the same
>> + * type are sorted by start address. Overlapping segments of the
>> + * same type are merged.
>>   */
>>  static int iommu_insert_resv_region(struct iommu_resv_region *new,
>>  				    struct list_head *regions)
>>  {
>> -	struct iommu_resv_region *region;
>> -	phys_addr_t start = new->start;
>> -	phys_addr_t end = new->start + new->length - 1;
>> -	struct list_head *pos = regions->next;
>> +	struct iommu_resv_region *iter, *tmp, *nr, *top;
>> +	struct list_head low, high, stack;
>> +	bool added = false;
>>
>> -	while (pos != regions) {
>> -		struct iommu_resv_region *entry =
>> -			list_entry(pos, struct iommu_resv_region, list);
>> -		phys_addr_t a = entry->start;
>> -		phys_addr_t b = entry->start + entry->length - 1;
>> -		int type = entry->type;
>> +	INIT_LIST_HEAD(&low);
>> +	INIT_LIST_HEAD(&high);
>> +	INIT_LIST_HEAD(&stack);
>>
>> -		if (end < a) {
>> -			goto insert;
>> -		} else if (start > b) {
>> -			pos = pos->next;
>> -		} else if ((start >= a) && (end <= b)) {
>> -			if (new->type == type)
>> -				return 0;
>> -			else
>> -				pos = pos->next;
>> -		} else {
>> -			if (new->type == type) {
>> -				phys_addr_t new_start = min(a, start);
>> -				phys_addr_t new_end = max(b, end);
>> -				int ret;
>> -
>> -				list_del(&entry->list);
>> -				entry->start = new_start;
>> -				entry->length = new_end - new_start + 1;
>> -				ret = iommu_insert_resv_region(entry, regions);
>> -				kfree(entry);
>> -				return ret;
>> -			} else {
>> -				pos = pos->next;
>> -			}
>> -		}
>> -	}
>> -insert:
>> -	region = iommu_alloc_resv_region(new->start, new->length,
>> -					 new->prot, new->type);
>> -	if (!region)
>> +	nr = iommu_alloc_resv_region(new->start, new->length,
>> +				     new->prot, new->type);
>> +	if (!nr)
>>  		return -ENOMEM;
>>
>> -	list_add_tail(&region->list, pos);
>> +	/*
>> +	 * Elements are dispatched into 3 lists: low/high contain
>> +	 * segments of lower/higher types than @new; only segments
>> +	 * with same type as @new remain in @regions, including @new
>> +	 * ordered inserted by start address
>> +	 */
>> +	list_for_each_entry_safe(iter, tmp, regions, list) {
>> +		if (iter->type < nr->type) {
>> +			list_move_tail(&iter->list, &low);
>> +		} else if (iter->type > nr->type) {
>> +			list_move_tail(&iter->list, &high);
>> +		} else if (nr->start <= iter->start && !added) {
>> +			list_add_tail(&nr->list, &iter->list);
>> +			added = true;
>> +		}
>> +	}
>> +	if (!added)
>> +		list_add_tail(&nr->list, regions);
>> +
>> +	/* Merge overlapping segments in @regions, if any */
>> +	list_move(regions->next, &stack); /* move the 1st elt to the stack */
>> +	list_for_each_entry_safe(iter, tmp, regions, list) {
>> +		phys_addr_t top_end, iter_end = iter->start + iter->length - 1;
>> +
>> +		top = list_last_entry(&stack, struct iommu_resv_region, list);
>> +		top_end = top->start + top->length - 1;
>> +
>> +		if (iter->start > top_end + 1) {
>> +			list_move(&iter->list, &top->list);
>> +		} else {
>> +			top->length = max(top_end, iter_end) - top->start + 1;
>> +			list_del(&iter->list);
>> +			kfree(iter);
>> +		}
>> +	}
>> +	list_splice(&stack, regions);
>> +	list_splice(&low, regions);
>> +	list_splice_tail(&high, regions);
>>  	return 0;
>>  }
>>
>> --
>> 2.20.1
>