linux-kernel - [PATCH 5.10 170/289] mm/gup: check every subpage of a compound page during isolation

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Date:   Mon, 17 May 2021 16:01:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pavel Tatashin <pasha.tatashin@...een.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>,
        James Morris <jmorris@...ei.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.10 170/289] mm/gup: check every subpage of a compound page during isolation

From: Pavel Tatashin <pasha.tatashin@...een.com>

[ Upstream commit 83c02c23d0747a7bdcd71f99a538aacec94b146c ]

When pages are isolated in check_and_migrate_movable_pages() we skip
compound number of pages at a time.  However, as Jason noted, it is not
necessary correct that pages[i] corresponds to the pages that we
skipped.  This is because it is possible that the addresses in this
range had split_huge_pmd()/split_huge_pud(), and these functions do not
update the compound page metadata.

The problem can be reproduced if something like this occurs:

1. User faulted huge pages.
2. split_huge_pmd() was called for some reason
3. User has unmapped some sub-pages in the range
4. User tries to longterm pin the addresses.

The resulting pages[i] might end-up having pages which are not compound
size page aligned.

Link: https://lkml.kernel.org/r/20210215161349.246722-3-pasha.tatashin@soleen.com
Fixes: aa712399c1e8 ("mm/gup: speed up check_and_migrate_cma_pages() on huge page")
Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
Reported-by: Jason Gunthorpe <jgg@...dia.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: James Morris <jmorris@...ei.org>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sasha Levin <sashal@...nel.org>
Cc: Steven Rostedt (VMware) <rostedt@...dmis.org>
Cc: Tyler Hicks <tyhicks@...ux.microsoft.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 mm/gup.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 054ff923d3d9..e10807c4c46b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1562,26 +1562,23 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
 					unsigned int gup_flags)
 {
 	unsigned long i;
-	unsigned long step;
 	bool drain_allow = true;
 	bool migrate_allow = true;
 	LIST_HEAD(cma_page_list);
 	long ret = nr_pages;
+	struct page *prev_head, *head;
 	struct migration_target_control mtc = {
 		.nid = NUMA_NO_NODE,
 		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_NOWARN,
 	};
 
 check_again:
-	for (i = 0; i < nr_pages;) {
-
-		struct page *head = compound_head(pages[i]);
-
-		/*
-		 * gup may start from a tail page. Advance step by the left
-		 * part.
-		 */
-		step = compound_nr(head) - (pages[i] - head);
+	prev_head = NULL;
+	for (i = 0; i < nr_pages; i++) {
+		head = compound_head(pages[i]);
+		if (head == prev_head)
+			continue;
+		prev_head = head;
 		/*
 		 * If we get a page from the CMA zone, since we are going to
 		 * be pinning these entries, we might as well move them out
@@ -1605,8 +1602,6 @@ check_again:
 				}
 			}
 		}
-
-		i += step;
 	}
 
 	if (!list_empty(&cma_page_list)) {
-- 
2.30.2