linux-kernel - [PATCH 03/21] mm/hugetlb: correct demote page offset logic

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Message-Id: <20220913195508.3511038-4-opendmb@gmail.com>
Date:   Tue, 13 Sep 2022 12:54:50 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jonathan Corbet <corbet@....net>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Rapoport <rppt@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Doug Berger <opendmb@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Oscar Salvador <osalvador@...e.de>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        - <devicetree-spec@...r.kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
        Mel Gorman <mgorman@...e.de>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux.dev
Subject: [PATCH 03/21] mm/hugetlb: correct demote page offset logic

With gigantic pages it may not be true that struct page structures
are contiguous across the entire gigantic page. The mem_map_offset
function is used here in place of direct pointer arithmetic to
correct for this.

Fixes: 8531fc6f52f5 ("hugetlb: add hugetlb demote page support")
Signed-off-by: Doug Berger <opendmb@...il.com>
---
 mm/hugetlb.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 79949893ac12..a1d51a1f0404 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3420,6 +3420,7 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
 {
 	int i, nid = page_to_nid(page);
 	struct hstate *target_hstate;
+	struct page *subpage;
 	int rc = 0;
 
 	target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
@@ -3453,15 +3454,16 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
 	mutex_lock(&target_hstate->resize_lock);
 	for (i = 0; i < pages_per_huge_page(h);
 				i += pages_per_huge_page(target_hstate)) {
+		subpage = mem_map_offset(page, i);
 		if (hstate_is_gigantic(target_hstate))
-			prep_compound_gigantic_page_for_demote(page + i,
+			prep_compound_gigantic_page_for_demote(subpage,
 							target_hstate->order);
 		else
-			prep_compound_page(page + i, target_hstate->order);
-		set_page_private(page + i, 0);
-		set_page_refcounted(page + i);
-		prep_new_huge_page(target_hstate, page + i, nid);
-		put_page(page + i);
+			prep_compound_page(subpage, target_hstate->order);
+		set_page_private(subpage, 0);
+		set_page_refcounted(subpage);
+		prep_new_huge_page(target_hstate, subpage, nid);
+		put_page(subpage);
 	}
 	mutex_unlock(&target_hstate->resize_lock);
 
-- 
2.25.1