mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage

PATCH Superseded Lance Yang 2 participants 4 messages Sep 30, 2025

Subsystems (3)

Stable branch Memory management MM migration

lore

Share & tools

lore

Lance Yang

author

2025-09-30 07:13 UTC #0 lore raw

PATCH v4 1/1 mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage

From: Lance Yang <[email protected]>

When splitting an mTHP and replacing a zero-filled subpage with the shared zeropage, try_to_map_unused_to_zeropage() currently drops several important PTE bits.

For userspace tools like CRIU, which rely on the soft-dirty mechanism for incremental snapshots, losing the soft-dirty bit means modified pages are missed, leading to inconsistent memory state after restore.

As pointed out by David, the more critical uffd-wp bit is also dropped. This breaks the userfaultfd write-protection mechanism, causing writes to be silently missed by monitoring applications, which can lead to data corruption.

Preserve both the soft-dirty and uffd-wp bits from the old PTE when creating the new zeropage mapping to ensure they are correctly tracked.

Cc <[email protected]>

Fixes b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp")

Suggested-by Dev Jain <[email protected]>

Acked-by David Hildenbrand <[email protected]>

Reviewed-by Dev Jain <[email protected]>

Signed-off-by Lance Yang <[email protected]>

---
v3 -> v4:
- Minor formatting tweak in try_to_map_unused_to_zeropage() function signature (per David and Dev)
- Collect Reviewed-by from Dev - thanks!
- https://lore.kernel.org/linux-mm/[email protected]/

v2 -> v3:
- ptep_get() gets called only once per iteration (per Dev)
- https://lore.kernel.org/linux-mm/[email protected]/

v1 -> v2:
- Avoid calling ptep_get() multiple times (per Dev)
- Double-check the uffd-wp bit (per David)
- Collect Acked-by from David - thanks!
- https://lore.kernel.org/linux-mm/[email protected]/

 mm/migrate.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

mm/migrate.c +10 -6

index ce83c2c3c287..21a2a1bf89f7 100644
@@ -296,8 +296,7 @@ bool isolate_folio_to_list(struct folio *folio, struct list_head *list)
 }
 
 static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
-					  struct folio *folio,
-					  unsigned long idx)
+		struct folio *folio, pte_t old_pte, unsigned long idx)
 {
 	struct page *page = folio_page(folio, idx);
 	pte_t newpte;

@@ -306,7 +305,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
 		return false;
 	VM_BUG_ON_PAGE(!PageAnon(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
+	VM_BUG_ON_PAGE(pte_present(old_pte), page);
 
 	if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) ||
 	    mm_forbids_zeropage(pvmw->vma->vm_mm))

@@ -322,6 +321,12 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
 
 	newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address),
 					pvmw->vma->vm_page_prot));
+
+	if (pte_swp_soft_dirty(old_pte))
+		newpte = pte_mksoft_dirty(newpte);
+	if (pte_swp_uffd_wp(old_pte))
+		newpte = pte_mkuffd_wp(newpte);
+
 	set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte);
 
 	dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio));

@@ -344,7 +349,7 @@ static bool remove_migration_pte(struct folio *folio,
 
 	while (page_vma_mapped_walk(&pvmw)) {
 		rmap_t rmap_flags = RMAP_NONE;
-		pte_t old_pte;
+		pte_t old_pte = ptep_get(pvmw.pte);
 		pte_t pte;
 		swp_entry_t entry;
 		struct page *new;

@@ -365,12 +370,11 @@ static bool remove_migration_pte(struct folio *folio,
 		}
 #endif
 		if (rmap_walk_arg->map_unused_to_zeropage &&
-		    try_to_map_unused_to_zeropage(&pvmw, folio, idx))
+		    try_to_map_unused_to_zeropage(&pvmw, folio, old_pte, idx))
 			continue;
 
 		folio_get(folio);
 		pte = mk_pte(new, READ_ONCE(vma->vm_page_prot));
-		old_pte = ptep_get(pvmw.pte);
 
 		entry = pte_to_swp_entry(old_pte);
 		if (!is_migration_entry_young(entry))

Signature · 1 line

2.49.0

Lance Yang

author

2025-09-30 07:30 UTC #1 lore raw

Quoted 82 lines · Lance Yang

From: Lance Yang <[email protected]>
When splitting an mTHP and replacing a zero-filled subpage with the shared zeropage, try_to_map_unused_to_zeropage() currently drops several important PTE bits.
For userspace tools like CRIU, which rely on the soft-dirty mechanism for incremental snapshots, losing the soft-dirty bit means modified pages are missed, leading to inconsistent memory state after restore.
As pointed out by David, the more critical uffd-wp bit is also dropped. This breaks the userfaultfd write-protection mechanism, causing writes to be silently missed by monitoring applications, which can lead to data corruption.
Preserve both the soft-dirty and uffd-wp bits from the old PTE when creating the new zeropage mapping to ensure they are correctly tracked.
Cc <[email protected]>
Fixes b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp")
Suggested-by David Hildenbrand <[email protected]>
Suggested-by Dev Jain <[email protected]>
Acked-by David Hildenbrand <[email protected]>
Reviewed-by Dev Jain <[email protected]>
Signed-off-by Lance Yang <[email protected]>
---
v3 -> v4:
- Minor formatting tweak in try_to_map_unused_to_zeropage() function signature (per David and Dev)
- Collect Reviewed-by from Dev - thanks!
- https://lore.kernel.org/linux-mm/[email protected]/
v2 -> v3:
- ptep_get() gets called only once per iteration (per Dev)
- https://lore.kernel.org/linux-mm/[email protected]/
v1 -> v2:
- Avoid calling ptep_get() multiple times (per Dev)
- Double-check the uffd-wp bit (per David)
- Collect Acked-by from David - thanks!
- https://lore.kernel.org/linux-mm/[email protected]/
  mm/migrate.c | 16 ++++++++++------
  1 file changed, 10 insertions(+), 6 deletions(-)
mm/migrate.c +8 -3
index ce83c2c3c287..21a2a1bf89f7 100644
@@ -296,8 +296,7 @@ bool isolate_folio_to_list(struct folio *folio, struct list_head *list)
  }
 
  static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
-					  struct folio *folio,
-					  unsigned long idx)
+		struct folio *folio, pte_t old_pte, unsigned long idx)
  {
  	struct page *page = folio_page(folio, idx);
  	pte_t newpte;
@@ -306,7 +305,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
  		return false;
  	VM_BUG_ON_PAGE(!PageAnon(page), page);
  	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
+	VM_BUG_ON_PAGE(pte_present(old_pte), page);
 
  	if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) ||
  	    mm_forbids_zeropage(pvmw->vma->vm_mm))
@@ -322,6 +321,12 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
 
  	newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address),
  					pvmw->vma->vm_page_prot));
+
+	if (pte_swp_soft_dirty(old_pte))
+		newpte = pte_mksoft_dirty(newpte);
+	if (pte_swp_uffd_wp(old_pte))
+		newpte = pte_mkuffd_wp(newpte);
+
  	set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte);
 
  	dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio));

mm/migrate.c static bool remove_migration_pte(struct folio *folio, · line 352

Quoted 5 lines

mm/migrate.c +1 -1

@@ -344,7 +349,7 @@ static bool remove_migration_pte(struct folio *folio,
 
  	while (page_vma_mapped_walk(&pvmw)) {
  		rmap_t rmap_flags = RMAP_NONE;
-		pte_t old_pte;
+		pte_t old_pte = ptep_get(pvmw.pte);

Oops, I just found a NULL pointer dereference bug in my changes to remove_migration_pte() when we encounter a PMD-mapped THP migration entry.

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
		/* PMD-mapped THP migration entry */
		if (!pvmw.pte) {
			VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
					!folio_test_pmd_mappable(folio), folio);
			remove_migration_pmd(&pvmw, new);
			continue;
		}

#endif

ptep_get() is called too early... before the !pvmw.pte check for PMD-mapped entries.

The initialization of old_pte must be moved to after that if block.

Sorry for the churn :(
Lance

Quoted 17 lines

mm/migrate.c +1 -2

  		pte_t pte;
  		swp_entry_t entry;
  		struct page *new;

@@ -365,12 +370,11 @@ static bool remove_migration_pte(struct folio *folio,
  		}
  #endif
  		if (rmap_walk_arg->map_unused_to_zeropage &&
-		    try_to_map_unused_to_zeropage(&pvmw, folio, idx))
+		    try_to_map_unused_to_zeropage(&pvmw, folio, old_pte, idx))
  			continue;
 
  		folio_get(folio);
  		pte = mk_pte(new, READ_ONCE(vma->vm_page_prot));
-		old_pte = ptep_get(pvmw.pte);
 
  		entry = pte_to_swp_entry(old_pte);
  		if (!is_migration_entry_young(entry))

syzbot ci

syzbot Tested-by [email protected] on v4 1/1

2025-09-30 11:16 UTC #2 lore raw

In reply to Lance Yang

syzbot ci has tested the following series

[v4] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
https://lore.kernel.org/all/[email protected]
* [PATCH v4 1/1] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage

and found the following issue:

general protection fault in remove_migration_pte

Full report is available here:
https://ci.syzbot.org/series/8cc7e52f-a859-4251-bd08-9787cdaf7928

***

general protection fault in remove_migration_pte

tree:      linux-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next
base:      262858079afde6d367ce3db183c74d8a43a0e83f
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/97ee4826-5d29-472d-a85d-51543b0e45de/config
C repro:   https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/c_repro
syz repro: https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 6025 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline]
RIP: 0010:remove_migration_pte+0x369/0x2320 mm/migrate.c:352
Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24
RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006
RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00
RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000
FS:  00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 rmap_walk_anon+0x553/0x730 mm/rmap.c:2855
 remove_migration_ptes mm/migrate.c:469 [inline]
 migrate_folio_move mm/migrate.c:1381 [inline]
 migrate_folios_move mm/migrate.c:1711 [inline]
 migrate_pages_batch+0x202e/0x35e0 mm/migrate.c:1967
 migrate_pages_sync mm/migrate.c:1997 [inline]
 migrate_pages+0x1bcc/0x2930 mm/migrate.c:2106
 migrate_to_node mm/mempolicy.c:1244 [inline]
 do_migrate_pages+0x5ee/0x800 mm/mempolicy.c:1343
 kernel_migrate_pages mm/mempolicy.c:1858 [inline]
 __do_sys_migrate_pages mm/mempolicy.c:1876 [inline]
 __se_sys_migrate_pages+0x544/0x650 mm/mempolicy.c:1872
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb18e18ec29
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdca5c9838 EFLAGS: 00000246 ORIG_RAX: 0000000000000100
RAX: ffffffffffffffda RBX: 00007fb18e3d5fa0 RCX: 00007fb18e18ec29
RDX: 0000200000000300 RSI: 0000000000000003 RDI: 0000000000000000
RBP: 00007fb18e211e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb18e3d5fa0 R14: 00007fb18e3d5fa0 R15: 0000000000000004
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline]
RIP: 0010:remove_migration_pte+0x369/0x2320 mm/migrate.c:352
Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24
RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006
RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00
RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000
FS:  00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	00 48 8d             	add    %cl,-0x73(%rax)
   3:	43 20 48 89          	rex.XB and %cl,-0x77(%r8)
   7:	44 24 68             	rex.R and $0x68,%al
   a:	49 8d 47 40          	lea    0x40(%r15),%rax
   e:	48 89 84 24 e8 00 00 	mov    %rax,0xe8(%rsp)
  15:	00
  16:	4c 89 64 24 48       	mov    %r12,0x48(%rsp)
  1b:	4c 8b b4 24 50 01 00 	mov    0x150(%rsp),%r14
  22:	00
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 f7             	mov    %r14,%rdi
  34:	e8 f8 3e ff ff       	call   0xffff3f31
  39:	49 8b 06             	mov    (%r14),%rax
  3c:	48                   	rex.W
  3d:	89                   	.byte 0x89
  3e:	44                   	rex.R
  3f:	24                   	.byte 0x24

***

If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message:

Tested-by [email protected]

---
This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at [email protected].

Lance Yang

author

2025-09-30 11:20 UTC #3 lore raw

Quoted 25 lines · syzbot ci

syzbot ci has tested the following series
[v4] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
https://lore.kernel.org/all/[email protected]
* [PATCH v4 1/1] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
and found the following issue:
general protection fault in remove_migration_pte
Full report is available here:
https://ci.syzbot.org/series/8cc7e52f-a859-4251-bd08-9787cdaf7928
***
general protection fault in remove_migration_pte
tree:      linux-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next
base:      262858079afde6d367ce3db183c74d8a43a0e83f
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/97ee4826-5d29-472d-a85d-51543b0e45de/config
C repro:   https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/c_repro
syz repro: https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/syz_repro

Quoted 2 lines

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]

This is a known issue that I introduced in the v3 patch. I spotted this exact NULL pointer dereference bug[1] myself and have already sent out a v5 version[2] with the fix.

The root cause is that ptep_get() is called before the !pwmw.pte check, which handles PMD-mapped THP migration entries.

[1] https://lore.kernel.org/linux-mm/[email protected]
[2] https://lore.kernel.org/linux-mm/[email protected]

Thanks,
Lance

Quoted 87 lines

CPU: 0 UID: 0 PID: 6025 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline]
RIP: 0010:remove_migration_pte+0x369/0x2320 mm/migrate.c:352
Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24
RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006
RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00
RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000
FS:  00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0
Call Trace:
  <TASK>
  rmap_walk_anon+0x553/0x730 mm/rmap.c:2855
  remove_migration_ptes mm/migrate.c:469 [inline]
  migrate_folio_move mm/migrate.c:1381 [inline]
  migrate_folios_move mm/migrate.c:1711 [inline]
  migrate_pages_batch+0x202e/0x35e0 mm/migrate.c:1967
  migrate_pages_sync mm/migrate.c:1997 [inline]
  migrate_pages+0x1bcc/0x2930 mm/migrate.c:2106
  migrate_to_node mm/mempolicy.c:1244 [inline]
  do_migrate_pages+0x5ee/0x800 mm/mempolicy.c:1343
  kernel_migrate_pages mm/mempolicy.c:1858 [inline]
  __do_sys_migrate_pages mm/mempolicy.c:1876 [inline]
  __se_sys_migrate_pages+0x544/0x650 mm/mempolicy.c:1872
  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb18e18ec29
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdca5c9838 EFLAGS: 00000246 ORIG_RAX: 0000000000000100
RAX: ffffffffffffffda RBX: 00007fb18e3d5fa0 RCX: 00007fb18e18ec29
RDX: 0000200000000300 RSI: 0000000000000003 RDI: 0000000000000000
RBP: 00007fb18e211e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb18e3d5fa0 R14: 00007fb18e3d5fa0 R15: 0000000000000004
  </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline]
RIP: 0010:remove_migration_pte+0x369/0x2320 mm/migrate.c:352
Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24
RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006
RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00
RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000
FS:  00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
    0:	00 48 8d             	add    %cl,-0x73(%rax)
    3:	43 20 48 89          	rex.XB and %cl,-0x77(%r8)
    7:	44 24 68             	rex.R and $0x68,%al
    a:	49 8d 47 40          	lea    0x40(%r15),%rax
    e:	48 89 84 24 e8 00 00 	mov    %rax,0xe8(%rsp)
   15:	00
   16:	4c 89 64 24 48       	mov    %r12,0x48(%rsp)
   1b:	4c 8b b4 24 50 01 00 	mov    0x150(%rsp),%r14
   22:	00
   23:	4c 89 f0             	mov    %r14,%rax
   26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
   2f:	74 08                	je     0x39
   31:	4c 89 f7             	mov    %r14,%rdi
   34:	e8 f8 3e ff ff       	call   0xffff3f31
   39:	49 8b 06             	mov    (%r14),%rax
   3c:	48                   	rex.W
   3d:	89                   	.byte 0x89
   3e:	44                   	rex.R
   3f:	24                   	.byte 0x24

***

If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message:

Tested-by [email protected]

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