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Date: Thu, 1 Aug 2019 16:24:26 +0200
From: Auger Eric <eric.auger@...hat.com>
To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
"eric.auger.pro@...il.com" <eric.auger.pro@...il.com>,
"joro@...tes.org" <joro@...tes.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"dwmw2@...radead.org" <dwmw2@...radead.org>,
"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
"robin.murphy@....com" <robin.murphy@....com>,
"hch@...radead.org" <hch@...radead.org>
Subject: Re: [PATCH] iommu: revisit iommu_insert_resv_region() implementation
Hi Shameer,
On 8/1/19 3:46 PM, Shameerali Kolothum Thodi wrote:
> Hi Eric,
>
>> -----Original Message-----
>> From: Eric Auger [mailto:eric.auger@...hat.com]
>> Sent: 30 July 2019 15:01
>> To: eric.auger.pro@...il.com; eric.auger@...hat.com; joro@...tes.org;
>> iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org;
>> dwmw2@...radead.org; alex.williamson@...hat.com;
>> robin.murphy@....com; hch@...radead.org
>> Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.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@...hat.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(®ion->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
>
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