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[parent not found: <20260213154336.434008-1-kartikey406@gmail.com>]
[parent not found: <20260209131144.33939-1-kartikey406@gmail.com>]
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[parent not found: <20260209015545.20766-1-kartikey406@gmail.com>]
* [PATCH] KVM: guest_memfd: Disable VMA merging with VM_DONTEXPAND
  2026-01-30 20:15 syzbot
@ 2026-02-04 17:01 Ackerley Tng
  2026-02-04 18:21 ` [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping syzbot
  -1 siblings, 1 reply; 16+ messages in thread
From: Ackerley Tng @ 2026-02-04 17:01 UTC (permalink / raw)
  To: syzbot+33a04338019ac7e43a44
  Cc: kvm, linux-kernel, pbonzini, syzkaller-bugs, Ackerley Tng

#syz test: git://git.kernel.org/pub/scm/virt/kvm/kvm.git next

guest_memfd VMAs don't need to be merged, especially now, since guest_memfd
only supports PAGE_SIZE folios.

Set VM_DONTEXPAND on guest_memfd VMAs.

In addition, this disables khugepaged from operating on guest_memfd folios,
which may result in unintended merging of guest_memfd folios.

Change-Id: I5867edcb66b075b54b25260afd22a198aee76df1
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 virt/kvm/guest_memfd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index fdaea3422c30..3d4ac461c28b 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -480,6 +480,12 @@ static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma)
 		return -EINVAL;
 	}

+	/*
+	 * Disable VMA merging - guest_memfd VMAs should be
+	 * static. This also stops khugepaged from operating on
+	 * guest_memfd VMAs and folios.
+	 */
+	vm_flags_set(vma, VM_DONTEXPAND);
 	vma->vm_ops = &kvm_gmem_vm_ops;

 	return 0;
--
2.53.0.rc2.204.g2597b5adb4-goog

^ permalink raw reply related	[flat|nested] 16+ messages in thread
[parent not found: <20260202151142.99116-1-kartikey406@gmail.com>]
[parent not found: <20260202083439.95644-1-kartikey406@gmail.com>]
[parent not found: <20260201110809.91962-1-kartikey406@gmail.com>]
[parent not found: <20260201074823.90148-1-kartikey406@gmail.com>]
[parent not found: <20260201054807.88100-1-kartikey406@gmail.com>]
[parent not found: <20260201045720.85957-1-kartikey406@gmail.com>]
* [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping
@ 2026-01-30 20:15 syzbot
  0 siblings, 0 replies; 16+ messages in thread
From: syzbot @ 2026-01-30 20:15 UTC (permalink / raw)
  To: kvm, linux-kernel, pbonzini, syzkaller-bugs

Hello,

syzbot found the following issue on:

HEAD commit:    1f97d9dcf536 Merge tag 'vfio-v6.19-rc8' of https://github...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10b3e322580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15e5ebfa580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13eef85a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f898291c4b7b/disk-1f97d9dc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cac48e20323c/vmlinux-1f97d9dc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d2e60d34b7e7/bzImage-1f97d9dc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com

------------[ cut here ]------------
folio_test_large(folio)
WARNING: arch/x86/kvm/../../../virt/kvm/guest_memfd.c:416 at kvm_gmem_fault_user_mapping+0x4b5/0x6e0 virt/kvm/guest_memfd.c:416, CPU#1: syz.3.124/6406
Modules linked in:
CPU: 1 UID: 0 PID: 6406 Comm: syz.3.124 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
RIP: 0010:kvm_gmem_fault_user_mapping+0x4b5/0x6e0 virt/kvm/guest_memfd.c:416
Code: 00 e9 a1 fe ff ff bd 00 04 00 00 eb d9 e8 43 b8 83 00 48 c7 c6 e0 9f 82 8b 48 89 df e8 d4 f8 ce 00 90 0f 0b e8 2c b8 83 00 90 <0f> 0b 90 48 8d 6b 34 48 89 df e8 ec f6 bb 00 be 04 00 00 00 48 89
RSP: 0018:ffffc90004ab7848 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffea00018a0000 RCX: ffffffff81834070
RDX: ffff888028b124c0 RSI: ffffffff81834334 RDI: ffff888028b124c0
RBP: ffffc90004ab79f8 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000040 R11: 0000000000000000 R12: ffffea00018a0000
R13: ffffc90004ab7a08 R14: 0000000000000040 R15: ffffea00018a0008
FS:  00007fb8562ce6c0(0000) GS:ffff8881246db000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f89fb863d58 CR3: 000000006060a000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __do_fault+0x10d/0x550 mm/memory.c:5323
 do_read_fault mm/memory.c:5758 [inline]
 do_fault+0xaf9/0x1990 mm/memory.c:5892
 do_pte_missing mm/memory.c:4404 [inline]
 handle_pte_fault mm/memory.c:6276 [inline]
 __handle_mm_fault+0x1807/0x2b50 mm/memory.c:6414
 handle_mm_fault+0x36d/0xa20 mm/memory.c:6583
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0xf9c/0x34d0 mm/gup.c:1428
 populate_vma_page_range+0x267/0x3f0 mm/gup.c:1860
 __mm_populate+0x107/0x3a0 mm/gup.c:1963
 do_mlock+0x3f0/0x7f0 mm/mlock.c:653
 __do_sys_mlock mm/mlock.c:661 [inline]
 __se_sys_mlock mm/mlock.c:659 [inline]
 __x64_sys_mlock+0x59/0x80 mm/mlock.c:659
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb85539aeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb8562ce028 EFLAGS: 00000246 ORIG_RAX: 0000000000000095
RAX: ffffffffffffffda RBX: 00007fb855615fa0 RCX: 00007fb85539aeb9
RDX: 0000000000000000 RSI: 0000000000800000 RDI: 0000200000000000
RBP: 00007fb855408c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb855616038 R14: 00007fb855615fa0 R15: 00007ffcc1750088
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

^ permalink raw reply	[flat|nested] 16+ messages in thread
end of thread, other threads:[~2026-02-13 16:10 UTC | newest]

Thread overview: 16+ messages (download: mbox.gz follow: Atom feed
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     [not found] <cover.1770148108.git.ackerleytng@google.com>
2026-02-03 22:50 ` [PATCH 1/2] KVM: guest_memfd: Always use order 0 when allocating for guest_memfd Ackerley Tng
2026-02-03 22:00   ` [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping syzbot
2026-02-04 12:36   ` [PATCH 1/2] KVM: guest_memfd: Always use order 0 when allocating for guest_memfd Deepanshu Kartikey
2026-02-04 16:30     ` Ackerley Tng
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2026-02-13 16:10 ` [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping syzbot
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2026-02-09 13:38 ` syzbot
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2026-02-09  2:34 ` syzbot
2026-02-04 17:01 [PATCH] KVM: guest_memfd: Disable VMA merging with VM_DONTEXPAND Ackerley Tng
2026-02-04 18:21 ` [syzbot] [kvm?] WARNING in kvm_gmem_fault_user_mapping syzbot
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2026-02-02 16:39 ` syzbot
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2026-02-01  6:25 ` syzbot
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