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

[Sean Christopherson]

On Thu, Oct 29, 2026, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c339f4010dea Merge tag 'platform-drivers-x86-v7.4-1' of gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15f440b1580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=119e5f4d0a8d39cf
> dashboard link: https://syzkaller.appspot.com/bug?extid=da2a2f350196c7a0a389
> 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=12952929580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-c339f401.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ff23ecfc810c/vmlinux-c339f401.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/6554a89077aa/bzImage-c339f401.xz
> 
> AI-generated root cause summary:
> When a VM is terminated or marked dead (e.g., via kvm_vm_dead() due to an error
> in enter_smm() or migration), the KVM_REQ_VM_DEAD request is raised on its
> vCPUs. If userspace subsequently issues the KVM_PRE_FAULT_MEMORY ioctl,
> kvm_tdp_page_prefault() bails out upon observing KVM_REQ_VM_DEAD and returns
> -EIO. However, kvm_vcpu_pre_fault_memory() in virt/kvm/kvm_main.c considers -EIO
> an unexpected internal condition and triggers WARN_ON_ONCE(r == 0 || r == -EIO).
> In a production kernel without panic_on_warn, execution breaks out of the loop
> and cleanly returns -EIO to userspace without crashing or corrupting memory.
> 
> full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=da2a2f350196c7a0a389
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+da2a2f350196c7a0a389@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> r == 0 || r == -EIO
> WARNING: arch/x86/kvm/../../../virt/kvm/kvm_main.c:4465 at kvm_vcpu_pre_fault_memory virt/kvm/kvm_main.c:4465 [inline], CPU#1: syz.0.17/6063
> WARNING: arch/x86/kvm/../../../virt/kvm/kvm_main.c:4465 at kvm_vcpu_ioctl+0x156a/0x17b0 virt/kvm/kvm_main.c:4744, CPU#1: syz.0.17/6063
> Modules linked in:
> CPU: 1 UID: 0 PID: 6063 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:kvm_vcpu_pre_fault_memory virt/kvm/kvm_main.c:4465 [inline]
> RIP: 0010:kvm_vcpu_ioctl+0x156a/0x17b0 virt/kvm/kvm_main.c:4744
> Code: 9c 35 8b 00 be 01 00 00 00 4c 89 f7 e8 4f b1 b5 03 e9 c3 f8 ff ff e8 85 35 8b 00 90 0f 0b 90 e9 2c f2 ff ff e8 77 35 8b 00 90 <0f> 0b 90 e9 38 fd ff ff e8 69 35 8b 00 65 48 8b 3d 99 02 36 14 31
> RSP: 0018:ffffc90003957c98 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 1ffff9200072af98 RCX: 0000000000000000
> RDX: ffff8880355fcb00 RSI: ffffffff81831d69 RDI: 0000000000000007
> RBP: ffff8880459f8048 R08: fffffffffffffffb R09: fffffffffffffffb
> R10: ffff8880459f803f R11: 0000000000000001 R12: fffffffffffffffb
> R13: ffffed1006abf960 R14: ffff8880459f8000 R15: ffffc90003957d70
> FS:  00007f7bf8c946c0(0000) GS:ffff8880d458e000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0b9aa1ee9c CR3: 0000000037636000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:597 [inline]
>  __se_sys_ioctl fs/ioctl.c:583 [inline]
>  __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7bf7d9f559
> 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:00007f7bf8c94028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f7bf8026090 RCX: 00007f7bf7d9f559
> RDX: 0000200000000800 RSI: 00000000c040aed5 RDI: 0000000000000005
> RBP: 00007f7bf7e36b20 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f7bf8026128 R14: 00007f7bf8026090 R15: 00007ffcdd24ea18
>  </TASK>

#syz dup: [syzbot] [kvm?] WARNING in kvm_vcpu_pre_fault_memory