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Subject: Re: kvm: WARNING in em_ret_far
To: Dmitry Vyukov <dvyukov@google.com>, rkrcmar@redhat.com,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>,
        KVM list <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Steve Rutherford <srutherford@google.com>
References: <CACT4Y+aeey6PkF4BYHhXDob8N03OyddHBgV9XuDUt36G4eeoVg@mail.gmail.com>
Cc: syzkaller <syzkaller@googlegroups.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <01ec7bcc-96cd-88f9-7c2b-37b655083f38@redhat.com>
Date: Sun, 13 Nov 2016 16:55:58 +0100
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Reproduced.

Paolo

On 12/11/2016 22:31, Dmitry Vyukov wrote:
> Hello,
> 
> The following program triggers WARNING in em_ret_far:
> https://gist.githubusercontent.com/dvyukov/12bc06a5f638d91953f94bcbe49bcc89/raw/6d863470808a695c085620664b7134864b2eb2a9/gistfile1.txt
> 
> On commit 015ed9433be2b476ec7e2e6a9a411a56e3b5b035 (Nov 11).
> 
> WARNING: CPU: 2 PID: 3668 at arch/x86/kvm/emulate.c:2217 em_ret_far+0x428/0x480
> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 2 PID: 3668 Comm: syz-executor Not tainted 4.9.0-rc4+ #49
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  ffff88006b32f618 ffffffff81c2e46b ffffffff83270ec0 ffff88006b32f6f0
>  ffffffff83225600 ffffffff8110a218 ffff88006b32f6e0 ffffffff81546463
>  0000000041b58ab3 ffffffff837cda55 ffffffff815462ac ffffffff815470e9
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff81c2e46b>] dump_stack+0xb3/0x118 lib/dump_stack.c:51
>  [<ffffffff81546463>] panic+0x1b7/0x3a3 kernel/panic.c:179
>  [<ffffffff8123e014>] __warn+0x1c4/0x1e0 kernel/panic.c:542
>  [<ffffffff8123e1fc>] warn_slowpath_null+0x2c/0x40 kernel/panic.c:585
>  [<ffffffff8110a218>] em_ret_far+0x428/0x480 arch/x86/kvm/emulate.c:2217
>  [<ffffffff8110a287>] em_ret_far_imm+0x17/0x70 arch/x86/kvm/emulate.c:2227
>  [<ffffffff81111baa>] x86_emulate_insn+0x87a/0x3730 arch/x86/kvm/emulate.c:5294
>  [<ffffffff810ad160>] x86_emulate_instruction+0x520/0x1ba0
> arch/x86/kvm/x86.c:5545
>  [<     inline     >] emulate_instruction arch/x86/include/asm/kvm_host.h:1116
>  [<     inline     >] complete_emulated_io arch/x86/kvm/x86.c:6870
>  [<ffffffff810aecc9>] complete_emulated_mmio+0x4e9/0x710 arch/x86/kvm/x86.c:6934
>  [<ffffffff810bbffa>] kvm_arch_vcpu_ioctl_run+0x3b7a/0x5a90
> arch/x86/kvm/x86.c:6978
>  [<ffffffff81060cee>] kvm_vcpu_ioctl+0x61e/0xdd0
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:2557
>  [<     inline     >] vfs_ioctl fs/ioctl.c:43
>  [<ffffffff816b03cc>] do_vfs_ioctl+0x18c/0x1040 fs/ioctl.c:679
>  [<     inline     >] SYSC_ioctl fs/ioctl.c:694
>  [<ffffffff816b130f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
>  [<ffffffff831f0dc1>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> reboot: cpu_has_vmx: ecx=80a02021 1
>