Re: [syzbot] [kvm?] WARNING in kvm_vcpu_pre_fault_memory

[Sean Christopherson]

On Sun, Oct 04, 2026, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ce1e0223d8ad Merge tag 'devicetree-fixes-for-7.3-2' of git..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1353dbf5580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9d4242cb1c54cdf7
> dashboard link: https://syzkaller.appspot.com/bug?extid=db7bd0f41c2a7e82d4ba
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14cdf6c9580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12cdf6c9580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/217b0c1b14ee/disk-ce1e0223.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/335343cc5803/vmlinux-ce1e0223.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/760ef2f39df0/bzImage-ce1e0223.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+db7bd0f41c2a7e82d4ba@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> r == 0 || r == -EIO
> WARNING: arch/x86/kvm/../../../virt/kvm/kvm_main.c:4389 at kvm_vcpu_pre_fault_memory+0x45d/0x470 virt/kvm/kvm_main.c:4389, CPU#1: syz-executor267/8523
> Modules linked in:
> CPU: 1 UID: 0 PID: 8523 Comm: syz-executor267 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
> RIP: 0010:kvm_vcpu_pre_fault_memory+0x45d/0x470 virt/kvm/kvm_main.c:4389
> Code: fe ff ff e8 85 2e 88 00 90 0f 0b 90 e9 0d ff ff ff e8 77 2e 88 00 e8 42 85 f3 ff eb 8f e8 6b 2e 88 00 eb 05 e8 64 2e 88 00 90 <0f> 0b 90 e9 a7 fe ff ff 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90
> RSP: 0018:ffffc900024dfc28 EFLAGS: 00010293
> RAX: ffffffff813fe025 RBX: ffffc900024dfe00 RCX: ffff88807fcc0000
> RDX: 0000000000000000 RSI: ffffffff8eaf6510 RDI: fffffffffffffffb
> RBP: dffffc0000000000 R08: ffff88807fcc0000 R09: 0000000000000002
> R10: fffffffffffffffb R11: 0000000000000000 R12: ffffc900024dfe00
> R13: ffff88807fcc0000 R14: 1ffff1100ff98000 R15: fffffffffffffffb
> FS:  00007f9c411186c0(0000) GS:ffff888124dc7000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f9c4116312d CR3: 0000000026a4a000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  kvm_vcpu_ioctl+0x8a6/0xfd0 virt/kvm/kvm_main.c:4668
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:597 [inline]
>  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f9c4118db49
> Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f9c411181d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f9c4123bb88 RCX: 00007f9c4118db49
> RDX: 0000200000000100 RSI: 00000000c040aed5 RDI: 0000000000000005
> RBP: 00007f9c4123bb80 R08: 38203a6b63617473 R09: 38203a6b63617473
> R10: 38203a6b63617473 R11: 0000000000000246 R12: 00007f9c4120b858
> R13: 0000200000000118 R14: 0000200000000100 R15: 0000200000000600
>  </TASK>

#syz test

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 108d42c5c1d6..31aba0c6f883 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4386,10 +4386,7 @@ static int kvm_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
 		}
 
 		r = kvm_arch_vcpu_pre_fault_memory(vcpu, range);
-		if (WARN_ON_ONCE(r == 0 || r == -EIO))
-			break;
-
-		if (r < 0)
+		if (WARN_ON_ONCE(!r) || r < 0)
 			break;
 
 		range->size -= r;