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Date:   Tue, 14 Feb 2017 21:31:53 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>, KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steve Rutherford <srutherford@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: kvm: WARNING In kvm_apic_accept_events

On Mon, Jan 23, 2017 at 5:29 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 23/01/2017 17:03, David Hildenbrand wrote:
>> Am 22.01.2017 um 09:52 schrieb Dmitry Vyukov:
>>> On Sat, Nov 12, 2016 at 2:56 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>> Hello,
>>>>
>>>> The following program triggers WARNING in kvm_apic_accept_events:
>>>> https://gist.githubusercontent.com/dvyukov/95b845a2e637485568ea1ef181a72370/raw/d90717dd67128b21715c5e794568a1600f613d97/gistfile1.txt
>>>>
>>>> On commit 015ed9433be2b476ec7e2e6a9a411a56e3b5b035 (Nov 11).
>>>>
>>>> ------------[ cut here ]------------
>>>> WARNING: CPU: 1 PID: 23523 at arch/x86/kvm/lapic.c:2330
>>>> kvm_apic_accept_events+0x3f6/0x460
>>>> Modules linked in:[   55.632648] CPU: 1 PID: 2812 Comm: a.out Not
>>>> tainted 4.9.0-rc4+ #41
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>>  ffff88006be77978 ffffffff81c2f79b 0000000000000000 0000000000000000
>>>>  ffffffff8322d6a0 ffffffff81127426 ffff88006be779c0 ffffffff8123ffef
>>>>  ffffffff811acc46 ffffffff0000091a ffffffff8322d6a0 000000000000091a
>>>> Call Trace:
>>>>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>>>>  [<ffffffff81c2f79b>] dump_stack+0xb3/0x118 lib/dump_stack.c:51
>>>>  [<ffffffff8123ffef>] __warn+0x19f/0x1e0 kernel/panic.c:550
>>>>  [<ffffffff812401fc>] warn_slowpath_null+0x2c/0x40 kernel/panic.c:585
>>>>  [<ffffffff81127426>] kvm_apic_accept_events+0x3f6/0x460
>>>> arch/x86/kvm/lapic.c:2330
>>>>  [<     inline     >] vcpu_block arch/x86/kvm/x86.c:6793
>>>>  [<     inline     >] vcpu_run arch/x86/kvm/x86.c:6828
>>>>  [<ffffffff810b8f20>] kvm_arch_vcpu_ioctl_run+0x1580/0x5a90
>>>> arch/x86/kvm/x86.c:6984
>>>>  [<ffffffff8106091e>] kvm_vcpu_ioctl+0x61e/0xdd0
>>>> arch/x86/kvm/../../../virt/kvm/kvm_main.c:2557
>>>>  [<     inline     >] vfs_ioctl fs/ioctl.c:43
>>>>  [<ffffffff816b16fc>] do_vfs_ioctl+0x18c/0x1040 fs/ioctl.c:679
>>>>  [<     inline     >] SYSC_ioctl fs/ioctl.c:694
>>>>  [<ffffffff816b263f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
>>>>  [<ffffffff831ebd01>] entry_SYSCALL_64_fastpath+0x1f/0xc2
>>>> arch/x86/entry/entry_64.S:209
>>>> ---[ end trace b2415ddd1b26dce6 ]---
>>>
>>>
>>> ping
>>>
>>
>> Our VCPU is in SMM mode but is switched into KVM_MP_STATE_INIT_RECEIVED.
>>
>> The relevant warning is (arch/x86/kvm/lapic.c:kvm_apic_accept_events())
>>
>> if (is_smm(vcpu)) {
>>         WARN_ON_ONCE(vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED);
>>         ....
>>
>> Something like that might help (untested):
>>
>>
>> From: David Hildenbrand <david@...hat.com>
>> Date: Mon, 23 Jan 2017 16:42:23 +0100
>> Subject: [PATCH] KVM: x86: fix illegal MP_STATE when in/entering SMM
>>
>> If we already entered/are about to enter SMM, don't allow
>> switching to INIT/SIPI_RECEIVED, otherwise the next call to
>> kvm_apic_accept_events() will report a warning.
>>
>> Fixes: cd7764fe9f73 ("KVM: x86: latch INITs while in system management mode")
>> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>  arch/x86/kvm/x86.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 57d8a85..06ffc91 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -7247,6 +7247,12 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>>           mp_state->mp_state != KVM_MP_STATE_RUNNABLE)
>>               return -EINVAL;
>>
>> +     /* INITs are latched while in SMM */
>> +     if ((is_smm(vcpu) || vcpu->arch.smi_pending) &&
>> +         (mp_state->mp_state == KVM_MP_STATE_SIPI_RECEIVED ||
>> +          mp_state->mp_state == KVM_MP_STATE_INIT_RECEIVED))
>> +             return -EINVAL;
>> +
>>       if (mp_state->mp_state == KVM_MP_STATE_SIPI_RECEIVED) {
>>               vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
>>               set_bit(KVM_APIC_SIPI, &vcpu->arch.apic->pending_events);
>>
>
> Looks good, thanks for analyzing it.  I'll try making a minimal testcase...


Any progress with this? Should we commit this as is?

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