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SubjectRE: [PATCH v2] iommu: revisit iommu_insert_resv_region() implementation
Date
Hi Eric,

> -----Original Message-----
> From: Eric Auger [mailto:eric.auger@redhat.com]
> Sent: 01 August 2019 17:00
> 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; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@huawei.com>; alex.williamson@redhat.com;
> robin.murphy@arm.com; hch@infradead.org
> Subject: [PATCH v2] 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. The elements are sorted by start address and then by
> type, if their start address match.
>
> 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").

I rerun this on D05 and seems to retain the order for msi type as before.

estuary:/$ cat /sys/kernel/iommu_groups/3/reserved_regions
0x0000000008000000 0x00000000080fffff msi
0x00000000c6010000 0x00000000c601ffff msi

FWIW,

Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>

Cheers,
Shameer


> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v1 -> v2:
> - adapt the algo so that we don't need to move elements of
> other types to different list and sort by address and then by
> type
> ---
> drivers/iommu/iommu.c | 107 +++++++++++++++++++++++-------------------
> 1 file changed, 59 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0c674d80c37f..4257b179fa54 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -229,60 +229,71 @@ 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 start address and overlapping segments
> + * of the same type are merged.
> */
> -static int iommu_insert_resv_region(struct iommu_resv_region *new,
> - struct list_head *regions)
> +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 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(&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);
> + /* First add the new elt based on start address sorting */
> + 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;
> + }
> + }
> + if (!added)
> + list_add_tail(&nr->list, regions);
> +
> + /* 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) {
> + 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);
> + }
> + }
> + list_splice(&stack, regions);
> return 0;
> }
>
> --
> 2.20.1

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