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AJvYcCU90Z2JLHu9MYuRuxb3iwDqprmfIBPWwAbz/lf0H+gzn2+TqnA/iH/ykZsrJE7Sw52jj2eB9n7P9+/Szb4=@vger.kernel.org X-Gm-Message-State: AOJu0YwOei+eMrMkUTUBvf2DaEjtidZadHr13FJ6J4oG10AE2I7P+sn1 FnWDyUI8656qUpdPMJ52rD9b8QEb9RqIBm+QM791PA0srTmgB3Jf5ofd8ME7JW0KKRxOVn9p1n/ pk9FCqw== X-Received: from pfnu10.prod.google.com ([2002:aa7:848a:0:b0:821:813f:e13f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:1c88:b0:81f:82b2:ecf8 with SMTP id d2e1a72fcca58-82317ed8d49mr159949b3a.63.1769105455159; Thu, 22 Jan 2026 10:10:55 -0800 (PST) Date: Thu, 22 Jan 2026 10:10:53 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <6925da1b.a70a0220.d98e3.00b0.GAE@google.com> <692611ac.a70a0220.2ea503.0091.GAE@google.com> Message-ID: Subject: Re: [syzbot] [kvm-x86?] WARNING in kvm_apic_accept_events (2) From: Sean Christopherson To: Alexander Potapenko Cc: syzbot , bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, pbonzini@redhat.com, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, x86@kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Thu, Jan 22, 2026, Alexander Potapenko wrote: > On Wed, Nov 26, 2025 at 12:10=E2=80=AFAM 'Sean Christopherson' via > syzkaller-bugs wrote: > > > > On Tue, Nov 25, 2025, syzbot wrote: > > > syzbot has found a reproducer for the following issue on: > > > > > > HEAD commit: 8a2bcda5e139 Merge tag 'for-6.18/dm-fixes' of git://g= it.ke.. > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D1604f8b45= 80000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=3Da1db0fea0= 40c2a9f > > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D59f2c3a3fc4= f6c09b8cd > > > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909= b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=3D13ecf61= 2580000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=3D13d9cf425= 80000 > > > > > > Downloadable assets: > > > disk image (non-bootable): https://storage.googleapis.com/syzbot-asse= ts/d900f083ada3/non_bootable_disk-8a2bcda5.raw.xz > > > vmlinux: https://storage.googleapis.com/syzbot-assets/fc3f96645396/vm= linux-8a2bcda5.xz > > > kernel image: https://storage.googleapis.com/syzbot-assets/e20aa7be5d= 33/bzImage-8a2bcda5.xz > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the = commit: > > > Reported-by: syzbot+59f2c3a3fc4f6c09b8cd@syzkaller.appspotmail.com > > > > > > ------------[ cut here ]------------ > > > WARNING: CPU: 0 PID: 5495 at arch/x86/kvm/lapic.c:3483 kvm_apic_accep= t_events+0x341/0x490 arch/x86/kvm/lapic.c:3483 > > > Modules linked in: > > > CPU: 0 UID: 0 PID: 5495 Comm: syz.0.17 Not tainted syzkaller #0 PREEM= PT(full) > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debia= n-1.16.3-2~bpo12+1 04/01/2014 > > > RIP: 0010:kvm_apic_accept_events+0x341/0x490 arch/x86/kvm/lapic.c:348= 3 > > > Code: eb 0c e8 32 da 71 00 eb 05 e8 2b da 71 00 45 31 ff 44 89 f8 5b = 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 10 da 71 00 90 <0f> 0b 90 e= 9 ec fd ff ff 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 4f > > > RSP: 0018:ffffc90002b2fbf0 EFLAGS: 00010293 > > > RAX: ffffffff814e3940 RBX: 0000000000000002 RCX: ffff88801f8ca480 > > > RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002 > > > RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff814689b6 > > > R10: dffffc0000000000 R11: ffffed1002268008 R12: 0000000000000002 > > > R13: dffffc0000000000 R14: ffff888042c95c00 R15: ffff8880113402d8 > > > FS: 000055558ab60500(0000) GS:ffff88808d72f000(0000) knlGS:000000000= 0000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 0000200000002000 CR3: 0000000058d0b000 CR4: 0000000000352ef0 > > > Call Trace: > > > > > > kvm_arch_vcpu_ioctl_get_mpstate+0x128/0x480 arch/x86/kvm/x86.c:12147 > > > kvm_vcpu_ioctl+0x625/0xe90 virt/kvm/kvm_main.c:4539 > > > 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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 > > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > RIP: 0033:0x7f918bd8f749 > > > 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 f= 0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 > > > RSP: 002b:00007ffc74a3c2a8 EFLAGS: 00000246 ORIG_RAX: 000000000000001= 0 > > > RAX: ffffffffffffffda RBX: 00007f918bfe5fa0 RCX: 00007f918bd8f749 > > > RDX: 0000000000000000 RSI: 000000008004ae98 RDI: 0000000000000005 > > > RBP: 00007f918be13f91 R08: 0000000000000000 R09: 0000000000000000 > > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > > R13: 00007f918bfe5fa0 R14: 00007f918bfe5fa0 R15: 0000000000000003 > > > > > > > Syzbot outsmarted me once again. I thought I had made this impossible = in commit > > 0fe3e8d804fd ("KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check= to KVM_RUN"), > > but now syzkaller is triggering the WARN by swapping the order and stuf= fing VMXON > > after INIT (ignore the EINVAL, KVM gets through enter_vmx_operation() b= efore detecting > > bad guest state). > > > > ioctl(5, KVM_SET_MP_STATE, 0x200000000000) =3D 0 > > ioctl(5, KVM_SET_NESTED_STATE, 0x200000000a80) =3D -1 EINVAL (Invalid= argument) > > ioctl(5, KVM_GET_MP_STATE, 0) =3D -1 EFAULT (Bad address) > > > > At this point, I'm leaning strongly towards dropping the WARN as it's n= ot helping, > > and userspace doing odd things is completely uninteresting. > > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > > index 7b1b8f450f4c..df2a69da11b7 100644 > > --- a/arch/x86/kvm/lapic.c > > +++ b/arch/x86/kvm/lapic.c > > @@ -3521,7 +3521,6 @@ int kvm_apic_accept_events(struct kvm_vcpu *vcpu) > > * wait-for-SIPI (WFS). > > */ > > if (!kvm_apic_init_sipi_allowed(vcpu)) { > > - WARN_ON_ONCE(vcpu->arch.mp_state =3D=3D KVM_MP_STATE_IN= IT_RECEIVED); > > clear_bit(KVM_APIC_SIPI, &apic->pending_events); > > return 0; > > } >=20 > Hi Sean, this is still biting us. > Have you made up your mind on the above patch? I'll properly post and apply the above. I have some ideas on how to preser= ve the basic gist of the sanity checks, though I hope I wrote them down somewh= ere, because I can't remember what they were...