On 13 Sep 2022, at 15:54, Doug Berger wrote:
> The function set_migratetype_isolate() has special handling for
> pageblocks of MIGRATE_CMA type that protects them from being
> isolated for MIGRATE_MOVABLE requests.
>
> Since isolate_single_pageblock() doesn't receive the migratetype
> argument of start_isolate_page_range() it used the migratetype
> of the pageblock instead of the requested migratetype which
> defeats this MIGRATE_CMA check.
>
> This allows an attempt to create a gigantic page within a CMA
> region to change the migratetype of the first and last pageblocks
> from MIGRATE_CMA to MIGRATE_MOVABLE when they are restored after
> failure, which corrupts the CMA region.
>
> The calls to (un)set_migratetype_isolate() for the first and last
> pageblocks of the start_isolate_page_range() are moved back into
> that function to allow access to its migratetype argument and make
> it easier to see how all of the pageblocks in the range are
> isolated.
>
> Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity")
> Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
> ---
> mm/page_isolation.c | 75 +++++++++++++++++++++------------------------
> 1 file changed, 35 insertions(+), 40 deletions(-)
Thanks for the fix.
Why not just pass migratetype into isolate_single_pageblock() and use
it when set_migratetype_isolate() is used? That would have much
fewer changes. What is the reason of pulling skip isolation logic out?
Ultimately, I would like to make MIGRATE_ISOLATE a separate bit,
so that migratetype will not be overwritten during page isolation.
Then, set_migratetype_isolate() and start_isolate_page_range()
will not have migratetype to set in error recovery any more.
That is on my TODO.
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 9d73dc38e3d7..8e16aa22cb61 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -286,8 +286,6 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * @flags: isolation flags
> * @gfp_flags: GFP flags used for migrating pages
> * @isolate_before: isolate the pageblock before the boundary_pfn
> - * @skip_isolation: the flag to skip the pageblock isolation in second
> - * isolate_single_pageblock()
> *
> * Free and in-use pages can be as big as MAX_ORDER-1 and contain more than one
> * pageblock. When not all pageblocks within a page are isolated at the same
> @@ -302,9 +300,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * the in-use page then splitting the free page.
> */
> static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
> - gfp_t gfp_flags, bool isolate_before, bool skip_isolation)
> + gfp_t gfp_flags, bool isolate_before)
> {
> - unsigned char saved_mt;
> unsigned long start_pfn;
> unsigned long isolate_pageblock;
> unsigned long pfn;
> @@ -328,18 +325,6 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
> start_pfn = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES),
> zone->zone_start_pfn);
>
> - saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
> -
> - if (skip_isolation)
> - VM_BUG_ON(!is_migrate_isolate(saved_mt));
> - else {
> - ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
> - isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
> -
> - if (ret)
> - return ret;
> - }
> -
> /*
> * Bail out early when the to-be-isolated pageblock does not form
> * a free or in-use page across boundary_pfn:
> @@ -428,7 +413,7 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
> ret = set_migratetype_isolate(page, page_mt,
> flags, head_pfn, head_pfn + nr_pages);
> if (ret)
> - goto failed;
> + return ret;
> }
>
> ret = __alloc_contig_migrate_range(&cc, head_pfn,
> @@ -443,7 +428,7 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
> unset_migratetype_isolate(page, page_mt);
>
> if (ret)
> - goto failed;
> + return -EBUSY;
> /*
> * reset pfn to the head of the free page, so
> * that the free page handling code above can split
> @@ -459,24 +444,19 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
> while (!PageBuddy(pfn_to_page(outer_pfn))) {
> /* stop if we cannot find the free page */
> if (++order >= MAX_ORDER)
> - goto failed;
> + return -EBUSY;
> outer_pfn &= ~0UL << order;
> }
> pfn = outer_pfn;
> continue;
> } else
> #endif
> - goto failed;
> + return -EBUSY;
> }
>
> pfn++;
> }
> return 0;
> -failed:
> - /* restore the original migratetype */
> - if (!skip_isolation)
> - unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
> - return -EBUSY;
> }
>
> /**
> @@ -534,21 +514,30 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> unsigned long isolate_start = ALIGN_DOWN(start_pfn, pageblock_nr_pages);
> unsigned long isolate_end = ALIGN(end_pfn, pageblock_nr_pages);
> int ret;
> - bool skip_isolation = false;
>
> /* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */
> - ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false, skip_isolation);
> + ret = set_migratetype_isolate(pfn_to_page(isolate_start), migratetype,
> + flags, isolate_start, isolate_start + pageblock_nr_pages);
> if (ret)
> return ret;
> -
> - if (isolate_start == isolate_end - pageblock_nr_pages)
> - skip_isolation = true;
> + ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false);
> + if (ret)
> + goto unset_start_block;
>
> /* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */
> - ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true, skip_isolation);
> + pfn = isolate_end - pageblock_nr_pages;
> + if (isolate_start != pfn) {
> + ret = set_migratetype_isolate(pfn_to_page(pfn), migratetype,
> + flags, pfn, pfn + pageblock_nr_pages);
> + if (ret)
> + goto unset_start_block;
> + }
> + ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true);
> if (ret) {
> - unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
> - return ret;
> + if (isolate_start != pfn)
> + goto unset_end_block;
> + else
> + goto unset_start_block;
> }
>
> /* skip isolated pageblocks at the beginning and end */
> @@ -557,15 +546,21 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> pfn += pageblock_nr_pages) {
> page = __first_valid_page(pfn, pageblock_nr_pages);
> if (page && set_migratetype_isolate(page, migratetype, flags,
> - start_pfn, end_pfn)) {
> - undo_isolate_page_range(isolate_start, pfn, migratetype);
> - unset_migratetype_isolate(
> - pfn_to_page(isolate_end - pageblock_nr_pages),
> - migratetype);
> - return -EBUSY;
> - }
> + start_pfn, end_pfn))
> + goto unset_isolated_blocks;
> }
> return 0;
> +
> +unset_isolated_blocks:
> + ret = -EBUSY;
> + undo_isolate_page_range(isolate_start + pageblock_nr_pages, pfn,
> + migratetype);
> +unset_end_block:
> + unset_migratetype_isolate(pfn_to_page(isolate_end - pageblock_nr_pages),
> + migratetype);
> +unset_start_block:
> + unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
> + return ret;
> }
>
> /*
> --
> 2.25.1
--
Best Regards,
Yan, Zi
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