linux-kernel - Re: stable/linux-4.14.y boot: 108 boots: 0 failed, 107 passed with 1 conflict (v4.14.11)

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Date:   Wed, 3 Jan 2018 12:14:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Guillaume Tucker <guillaume.tucker@...labora.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-build-reports@...ts.linaro.org,
        Matt Hart <matthew.hart@...aro.org>, stable@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, qemu-devel@...gnu.org
Subject: Re: stable/linux-4.14.y boot: 108 boots: 0 failed, 107 passed with 1
 conflict (v4.14.11)

On 03/01/2018 11:36, Thomas Gleixner wrote:
> On Wed, 3 Jan 2018, Guillaume Tucker wrote:
>> On 03/01/18 09:48, Thomas Gleixner wrote:
>>>> Well, it turns out this is not exactly a conflict as there's a
>>>> subtle difference between the qemu devices in lab-mhart and in
>>>> lab-collabora.  The ones in lab-collabora are configured to use
>>>> KVM, and it looks like the ones in lab-mhart aren't.
>>>>
>>>> So this job with KVM enabled passes in lab-collabora:
>>>>
>>>>    https://lava.collabora.co.uk/scheduler/job/1032358
>>>>
>>>> but it fails if I tell LAVA (qemu) to disable KVM:
>>>>
>>>>    https://lava.collabora.co.uk/scheduler/job/1032359
>>>>
>>>> with the same panic as in lab-mhart.  It seems like it's failing
>>>> to return from an interrupt:
>>>>
>>>>    http://lava.streamtester.net/scheduler/job/87308
>>>>
>>>>    [    2.678828]  ? native_iret+0x7/0x7
>>>>    [    2.679208] WARNING: can't dereference iret registers at
>>>> 00000000ffc66068
>>>> for ip page_fault+0x11/0x60
>>>>
>>>> This triggered an automated bisection on kernelci.org, please see
>>>> the results below.
>>>>
>>>> I may run another bisection with this config enabled earlier in
>>>> the history to track down the actual change in the code that
>>>> introduced the issue, let me know if it's worth doing.
>>>
>>> No, because before that commit not all pieces are in place.
>>>
>>> Can you please try the failing kernel with pti=off on the command line?
>>
>> It does boot with pti=off (and KVM disabled):
>>
>>   https://lava.collabora.co.uk/scheduler/job/1032387
> 
> So it's a qemu issue. Added qemu folks on Cc.

Reproduced, thanks.  I will look into it.

Paolo