On Tue, Nov 10, 2020 at 08:32:40PM +0100, David Hildenbrand wrote:
> commit 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and
> init_on_free=1 boot options") resulted with init_on_alloc=1 in all pages
> leaving the buddy via alloc_pages() and friends to be
> initialized/cleared/zeroed on allocation.
>
> However, the same logic is currently not applied to
> alloc_contig_pages(): allocated pages leaving the buddy aren't cleared
> with init_on_alloc=1 and init_on_free=0. Let's also properly clear
> pages on that allocation path and add support for __GFP_ZERO.
>
> With this change, we will see double clearing of pages in some
> cases. One example are gigantic pages (either allocated via CMA, or
> allocated dynamically via alloc_contig_pages()) - which is the right
> thing to do (and to be optimized outside of the buddy in the callers) as
> discussed in:
> https://lkml.kernel.org/r/[email protected]
>
> This change implies that with init_on_alloc=1
> - All CMA allocations will be cleared
> - Gigantic pages allocated via alloc_contig_pages() will be cleared
> - virtio-mem memory to be unplugged will be cleared. While this is
> suboptimal, it's similar to memory balloon drivers handling, where
> all pages to be inflated will get cleared as well.
>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Potapenko <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Mike Kravetz <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> mm/page_alloc.c | 24 +++++++++++++++++++++---
> 1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index eed4f4075b3c..0361b119b74e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8453,6 +8453,19 @@ static int __alloc_contig_migrate_range(struct
> compact_control *cc,
> return 0;
> }
>
> +static void __alloc_contig_clear_range(unsigned long start_pfn,
> + unsigned long end_pfn)
Maybe clear_contig_range() ?
> +{
> + unsigned long pfn;
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES) {
> + cond_resched();
> + kernel_init_free_pages(pfn_to_page(pfn),
> + min_t(unsigned long, end_pfn - pfn,
> + MAX_ORDER_NR_PAGES));
> + }
> +}
> +
> /**
> * alloc_contig_range() -- tries to allocate given range of pages
> * @start: start PFN to allocate
> @@ -8461,7 +8474,8 @@ static int __alloc_contig_migrate_range(struct
> compact_control *cc,
> * #MIGRATE_MOVABLE or #MIGRATE_CMA). All pageblocks
> * in range must have the same migratetype and it must
> * be either of the two.
> - * @gfp_mask: GFP mask to use during compaction
> + * @gfp_mask: GFP mask to use during compaction. __GFP_ZERO clears
> allocated
> + * pages.
"__GFP_ZERO is not passed to compaction but rather clears allocated pages"
> *
> * The PFN range does not have to be pageblock or MAX_ORDER_NR_PAGES
> * aligned. The PFN range must belong to a single zone.
> @@ -8488,7 +8502,7 @@ int alloc_contig_range(unsigned long start, unsigned
> long end,
> .mode = MIGRATE_SYNC,
> .ignore_skip_hint = true,
> .no_set_skip_hint = true,
> - .gfp_mask = current_gfp_context(gfp_mask),
> + .gfp_mask = current_gfp_context(gfp_mask & ~__GFP_ZERO),
> .alloc_contig = true,
> };
> INIT_LIST_HEAD(&cc.migratepages);
> @@ -8600,6 +8614,9 @@ int alloc_contig_range(unsigned long start, unsigned
> long end,
> if (end != outer_end)
> free_contig_range(end, outer_end - end);
>
> + if (!want_init_on_free() && want_init_on_alloc(gfp_mask))
> + __alloc_contig_clear_range(start, end);
> +
> done:
> undo_isolate_page_range(pfn_max_align_down(start),
> pfn_max_align_up(end), migratetype);
> @@ -8653,7 +8670,8 @@ static bool zone_spans_last_pfn(const struct zone *zone,
> /**
> * alloc_contig_pages() -- tries to find and allocate contiguous range of
> pages
> * @nr_pages: Number of contiguous pages to allocate
> - * @gfp_mask: GFP mask to limit search and used during compaction
> + * @gfp_mask: GFP mask to limit search and used during compaction.
> __GFP_ZERO
> + * clears allocated pages.
> * @nid: Target node
> * @nodemask: Mask for other possible nodes
> *
> --
> 2.26.2
>
--
Sincerely yours,
Mike.
