Re: [moderation/CI] Re: KVM: x86/hyperv: Fix racy usage of vcpu->arch.hyperv

#syz upstream

On Sat, Jun 13, 2026 at 10:32 PM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v2] KVM: x86/hyperv: Fix racy usage of vcpu->arch.hyperv
> https://lore.kernel.org/all/[email protected]
> * [PATCH v2 1/8] KVM: x86/hyperv: Get target FIFO in hv_tlb_flush_enqueue(), not caller
> * [PATCH v2 2/8] KVM: x86/hyperv: Check for NULL vCPU Hyper-V object in kvm_hv_get_tlb_flush_fifo()
> * [PATCH v2 3/8] KVM: x86/hyperv: Ensure vCPU's Hyper-V object is initialized on cross-vCPU accesses
> * [PATCH v2 4/8] KVM: Initialize a vCPU's index to '-1' while it's being created
> * [PATCH v2 5/8] KVM: Move nVMX's lockdep logic for vcpu->mutex to a common helper
> * [PATCH v2 6/8] KVM: x86: Treat a vCPU as unreachable if its index is invalid
> * [PATCH v2 7/8] KVM: x86/hyperv: Assert vCPU's mutex is held in to_hv_vcpu()
> * [PATCH v2 8/8] KVM: x86/hyperv: Use {READ,WRITE}_ONCE for cross-task synic->active accesses
>
> and found the following issue:
> WARNING in kvm_hv_vcpu_uninit
>
> Full report is available here:
> https://ci.syzbot.org/series/674ef35a-9335-4710-8a6d-b18d01510cbb
>
> ***
>
> WARNING in kvm_hv_vcpu_uninit
>
> tree:      linux-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next
> base:      c1f7303302927f9cbf4efedf70f0512cde168c65
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/20dd789e-0a89-4465-844c-9d91b5ce4a45/config
> syz repro: https://ci.syzbot.org/findings/eeefcfe6-b8e9-4c5b-900e-855d814f5d97/syz_repro
>
> ------------[ cut here ]------------
> debug_locks && !(lock_is_held(&(&vcpu->mutex)->dep_map) || vcpu->vcpu_idx < 0 || !refcount_read(&vcpu->kvm->users_count))
> WARNING: ./include/linux/kvm_host.h:996 at kvm_lockdep_assert_vcpu_is_locked_or_unreachable include/linux/kvm_host.h:994 [inline], CPU#1: syz.1.25/5883
> WARNING: ./include/linux/kvm_host.h:996 at to_hv_vcpu arch/x86/kvm/hyperv.h:78 [inline], CPU#1: syz.1.25/5883
> WARNING: ./include/linux/kvm_host.h:996 at kvm_hv_vcpu_uninit+0x198/0x210 arch/x86/kvm/hyperv.c:906, CPU#1: syz.1.25/5883
> Modules linked in:
> CPU: 1 UID: 0 PID: 5883 Comm: syz.1.25 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:kvm_lockdep_assert_vcpu_is_locked_or_unreachable include/linux/kvm_host.h:994 [inline]
> RIP: 0010:to_hv_vcpu arch/x86/kvm/hyperv.h:78 [inline]
> RIP: 0010:kvm_hv_vcpu_uninit+0x198/0x210 arch/x86/kvm/hyperv.c:906
> Code: 48 89 df e8 0a ba d8 00 48 c7 03 00 00 00 00 eb 05 e8 1c 63 6d 00 5b 41 5c 41 5e 41 5f 5d e9 8f f6 51 0a cc e8 09 63 6d 00 90 <0f> 0b 90 e9 65 ff ff ff 48 c7 c1 e0 5c 30 90 80 e1 07 80 c1 03 38
> RSP: 0018:ffffc900035ef940 EFLAGS: 00010293
> RAX: ffffffff8158f397 RBX: ffff88816987d400 RCX: ffff888110b20000
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000001 R08: ffff88810c5b9703 R09: 1ffff110218b72e0
> R10: dffffc0000000000 R11: ffffed10218b72e1 R12: 0000000000000000
> R13: 00000000fffffff8 R14: ffff88810c5b9700 R15: dffffc0000000000
> FS:  00007fbc073dc6c0(0000) GS:ffff8882a929a000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f451a40fff8 CR3: 000000010f703000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  kvm_arch_vcpu_destroy+0x1a9/0x380 arch/x86/kvm/x86.c:12905
>  kvm_vm_ioctl_create_vcpu+0x68b/0x940 virt/kvm/kvm_main.c:4262
>  kvm_vm_ioctl+0x893/0xd50 virt/kvm/kvm_main.c:5161
>  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:63 [inline]
>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fbc0659ce59
> 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:00007fbc073dc028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fbc06815fa0 RCX: 00007fbc0659ce59
> RDX: 0000000000000001 RSI: 000000000000ae41 RDI: 00000000000000f7
> RBP: 00007fbc06632d6f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fbc06816038 R14: 00007fbc06815fa0 R15: 00007fffc5de9fc8
>  </TASK>
>
>
> ***
>
> 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].
>
> To test a patch for this bug, please reply with `#syz test`
> (should be on a separate line).
>
> The patch should be attached to the email.
> Note: arguments like custom git repos and branches are not supported.
>
> The email will later be sent to:
> [[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]]
>
> If the report looks fine to you, reply with:
> #syz upstream
>
> If the report is a false positive, reply with
> #syz invalid
>
> --
> You received this message because you are subscribed to the Google Groups "syzkaller-upstream-moderation" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
> To view this discussion visit https://groups.google.com/d/msgid/syzkaller-upstream-moderation/6a2dbe63.8812e0fc.3c3fa4.0009.GAE%40google.com.