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SubjectRE: [PATCH v2 RESEND 2/4] Drivers: hv: balloon: account for gaps in hot add regions
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> @@ -676,35 +686,63 @@ static void hv_mem_hot_add(unsigned long start,
> unsigned long size,
>
> static void hv_online_page(struct page *pg) {
> - struct list_head *cur;
> struct hv_hotadd_state *has;
> + struct hv_hotadd_gap *gap;
> unsigned long cur_start_pgp;
> unsigned long cur_end_pgp;
> + bool is_gap = false;
>
> list_for_each(cur, &dm_device.ha_region_list) {
> has = list_entry(cur, struct hv_hotadd_state, list);
> cur_start_pgp = (unsigned long)
> + pfn_to_page(has->start_pfn);
> + cur_end_pgp = (unsigned long)pfn_to_page(has->end_pfn);
> +
> + /* The page belongs to a different HAS. */
> + if (((unsigned long)pg < cur_start_pgp) ||
> + ((unsigned long)pg >= cur_end_pgp))
> + continue;
> +
> + cur_start_pgp = (unsigned long)
> pfn_to_page(has->covered_start_pfn);
> cur_end_pgp = (unsigned long)pfn_to_page(has-
> >covered_end_pfn);
>
> - if (((unsigned long)pg >= cur_start_pgp) &&
> - ((unsigned long)pg < cur_end_pgp)) {
> - /*
> - * This frame is currently backed; online the
> - * page.
> - */
> - __online_page_set_limits(pg);
> - __online_page_increment_counters(pg);
> - __online_page_free(pg);
> + /* The page is not backed. */
> + if (((unsigned long)pg < cur_start_pgp) ||
> + ((unsigned long)pg >= cur_end_pgp))
> + continue;
> +
> + /* Check for gaps. */
> + list_for_each_entry(gap, &has->gap_list, list) {
> + cur_start_pgp = (unsigned long)
> + pfn_to_page(gap->start_pfn);
> + cur_end_pgp = (unsigned long)
> + pfn_to_page(gap->end_pfn);
> + if (((unsigned long)pg >= cur_start_pgp) &&
> + ((unsigned long)pg < cur_end_pgp)) {
> + is_gap = true;
> + break;
> + }
> }
> +
> + if (is_gap)
> + break;
> +
> + /* This frame is currently backed; online the page. */
> + __online_page_set_limits(pg);
> + __online_page_increment_counters(pg);
> + __online_page_free(pg);
> + break;
> }
> }
>

We may need to add similar logic to check for gaps in hv_bring_pgs_online().

[...]
> static unsigned long handle_pg_range(unsigned long pg_start, @@ -834,13
> +881,19 @@ static unsigned long process_hot_add(unsigned long pg_start,
> unsigned long rg_size)
> {
> struct hv_hotadd_state *ha_region = NULL;
> + int covered;
>
> if (pfn_cnt == 0)
> return 0;
>
> - if (!dm_device.host_specified_ha_region)
> - if (pfn_covered(pg_start, pfn_cnt))
> + if (!dm_device.host_specified_ha_region) {
> + covered = pfn_covered(pg_start, pfn_cnt);
> + if (covered < 0)
> + return 0;

If the hot-add pages aren't covered by any region, then shouldn't it fall through instead of returning?
That way the new ha_region can be added to the list and we hot-add the pages accordingly.

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