linux-kernel - [PATCH v1] mm/page_alloc: clear pages in alloc_contig_pages() with init_on_alloc=1 or __GFP

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Date:   Tue, 10 Nov 2020 20:32:40 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Oscar Salvador <osalvador@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH v1] mm/page_alloc: clear pages in alloc_contig_pages() with init_on_alloc=1 or __GFP_ZERO

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/20201019182853.7467-1-gpiccoli@canonical.com

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 <akpm@...ux-foundation.org>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Rapoport <rppt@...ux.ibm.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Kees Cook <keescook@...omium.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 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)
+{
+	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.
  *
  * 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