linux-kernel - [PATCH] mm: Avoid using set_pte_at when updating a present pte

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Message-Id: <20201008092541.398079-1-aneesh.kumar@linux.ibm.com>
Date:   Thu,  8 Oct 2020 14:55:41 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au
Cc:     npiggin@...il.com, "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.com>,
        Kirill Shutemov <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] mm: Avoid using set_pte_at when updating a present pte

This avoids the below warning

WARNING: CPU: 0 PID: 30613 at arch/powerpc/mm/pgtable.c:185 set_pte_at+0x2a8/0x3a0 arch/powerpc/mm/pgtable.c:185
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 30613 Comm: syz-executor.0 Not tainted 5.9.0-rc8-syzkaller-00156-gc85fb28b6f99 #0
Call Trace:
 [c0000000001cd1f0] panic+0x29c/0x75c kernel/panic.c:231
 [c0000000001cce24] __warn+0x104/0x1b8 kernel/panic.c:600
 [c000000000d829e4] report_bug+0x1d4/0x380 lib/bug.c:198
 [c000000000036800] program_check_exception+0x4e0/0x750 arch/powerpc/kernel/traps.c:1508
 [c0000000000098a8] program_check_common_virt+0x308/0x360
--- interrupt: 700 at set_pte_at+0x2a8/0x3a0 arch/powerpc/mm/pgtable.c:185
    LR = set_pte_at+0x2a4/0x3a0 arch/powerpc/mm/pgtable.c:185
 [c0000000005d2a7c] copy_present_page mm/memory.c:857 [inline]
 [c0000000005d2a7c] copy_present_pte mm/memory.c:899 [inline]
 [c0000000005d2a7c] copy_pte_range mm/memory.c:1014 [inline]
 [c0000000005d2a7c] copy_pmd_range mm/memory.c:1092 [inline]
 [c0000000005d2a7c] copy_pud_range mm/memory.c:1127 [inline]
 [c0000000005d2a7c] copy_p4d_range mm/memory.c:1150 [inline]
 [c0000000005d2a7c] copy_page_range+0x1f6c/0x2cc0 mm/memory.c:1212
 [c0000000001c63cc] dup_mmap kernel/fork.c:592 [inline]
 [c0000000001c63cc] dup_mm+0x77c/0xab0 kernel/fork.c:1355
 [c0000000001c8f70] copy_mm kernel/fork.c:1411 [inline]
 [c0000000001c8f70] copy_process+0x1f00/0x2740 kernel/fork.c:2070
 [c0000000001c9b54] _do_fork+0xc4/0x10b0 kernel/fork.c:2429
 [c0000000001caf54] __do_sys_clone3+0x1d4/0x2b0 kernel/fork.c:27

Architecture like ppc64 expects set_pte_at to be not used for updating a
valid pte. This is further explained in
commit 56eecdb912b5 ("mm: Use ptep/pmdp_set_numa() for updating _PAGE_NUMA bit")

Cc: Peter Xu <peterx@...hat.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jan Kara <jack@...e.cz>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Kirill Shutemov <kirill@...temov.name>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index fcfc4ca36eba..bfe202ef6244 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -854,7 +854,7 @@ copy_present_page(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	 * source pte back to being writable.
 	 */
 	if (pte_write(pte))
-		set_pte_at(src_mm, addr, src_pte, pte);
+		ptep_set_access_flags(vma, addr, src_pte, pte, 1);
 
 	new_page = *prealloc;
 	if (!new_page)
-- 
2.26.2