linux-kernel - [PATCH 5.4 303/340] hugetlb: fix update_and_free

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Date:   Mon,  1 Mar 2021 17:14:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zi Yan <ziy@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Davidlohr Bueso <dbueso@...e.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Joao Martins <joao.m.martins@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.4 303/340] hugetlb: fix update_and_free_page contig page struct assumption

From: Mike Kravetz <mike.kravetz@...cle.com>

commit dbfee5aee7e54f83d96ceb8e3e80717fac62ad63 upstream.

page structs are not guaranteed to be contiguous for gigantic pages.  The
routine update_and_free_page can encounter a gigantic page, yet it assumes
page structs are contiguous when setting page flags in subpages.

If update_and_free_page encounters non-contiguous page structs, we can see
“BUG: Bad page state in process …” errors.

Non-contiguous page structs are generally not an issue.  However, they can
exist with a specific kernel configuration and hotplug operations.  For
example: Configure the kernel with CONFIG_SPARSEMEM and
!CONFIG_SPARSEMEM_VMEMMAP.  Then, hotplug add memory for the area where
the gigantic page will be allocated.  Zi Yan outlined steps to reproduce
here [1].

[1] https://lore.kernel.org/linux-mm/16F7C58B-4D79-41C5-9B64-A1A1628F4AF2@nvidia.com/

Link: https://lkml.kernel.org/r/20210217184926.33567-1-mike.kravetz@oracle.com
Fixes: 944d9fec8d7a ("hugetlb: add support for gigantic page allocation at runtime")
Signed-off-by: Zi Yan <ziy@...dia.com>
Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Zi Yan <ziy@...dia.com>
Cc: Davidlohr Bueso <dbueso@...e.de>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Joao Martins <joao.m.martins@...cle.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/hugetlb.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1192,14 +1192,16 @@ static inline void destroy_compound_giga
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
+	struct page *subpage = page;
 
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[page_to_nid(page)]--;
-	for (i = 0; i < pages_per_huge_page(h); i++) {
-		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
+	for (i = 0; i < pages_per_huge_page(h);
+	     i++, subpage = mem_map_next(subpage, page, i)) {
+		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
 				1 << PG_referenced | 1 << PG_dirty |
 				1 << PG_active | 1 << PG_private |
 				1 << PG_writeback);