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Subject: Re: kvm crash on 5.7-rc1 and later
To:     Peter Zijlstra <peterz@infradead.org>,
        Woody Suwalski <terraluna977@gmail.com>
Cc:     pbonzini@redhat.com, LKML <linux-kernel@vger.kernel.org>,
        fenghua.yu@intel.com, Thomas Gleixner <tglx@linutronix.de>,
        Sean Christopherson <sean.j.christopherson@intel.com>
References: <9178ae3e-db32-c64b-7caf-737f3bc3ba8e@gmail.com>
 <20200711182158.GF597537@hirez.programming.kicks-ass.net>
From:   Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <b1d4e747-0c6d-b9f8-d795-1f4ed9e2420b@intel.com>
Date:   Sun, 12 Jul 2020 14:27:59 +0800
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On 7/12/2020 2:21 AM, Peter Zijlstra wrote:
> On Fri, Jul 03, 2020 at 11:15:31AM -0400, Woody Suwalski wrote:
>> I am observing a 100% reproducible kvm crash on kernels starting with
>> 5.7-rc1, always with the same opcode 0000.
>> It happens during wake up from the host suspended state. Worked OK on 5.6
>> and older.
>> The host is based on Debian testing, Thinkpad T440, i5 cpu.
>>
>> [   61.576664] kernel BUG at arch/x86/kvm/x86.c:387!
>> [   61.576672] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
>> [   61.576678] CPU: 0 PID: 3851 Comm: qemu-system-x86 Not tainted 5.7-pingu
>> #0
>> [   61.576680] Hardware name: LENOVO 20B6005JUS/20B6005JUS, BIOS GJETA4WW
>> (2.54 ) 03/27/2020
>> [   61.576700] RIP: 0010:kvm_spurious_fault+0xa/0x10 [kvm]
>>
>> Crash results in a dead kvm and occasionally a very unstable system.
>>
>> Bisecting the problem between v5.6 and v5.7-rc1 points to
>>
>> commit 6650cdd9a8ccf00555dbbe743d58541ad8feb6a7
>> Author: Peter Zijlstra (Intel) <peterz@infradead.org>
>> Date:   Sun Jan 26 12:05:35 2020 -0800
>>
>>      x86/split_lock: Enable split lock detection by kernel
>>
>> Reversing that patch seems to actually "cure" the issue.
>>
>> The problem is present in all kernels past 5.7-rc1, however the patch is not
>> reversing directly in later source trees, so can not retest the logic on
>> recent kernels.
>>
>> Peter, would you have idea how to debug that (or even better - would you
>> happen to know the fix)?
>>
>> I have attached dmesg logs from a "good" 5.6.9 kernel, and then "bad" 5.7.0
>> and 5.8-rc3
> 
> I have no clue about kvm. Nor do I actually have hardware with SLD on.
> I've Cc'ed a bunch of folks who might have more ideas.
> 

I think this bug is the same as the one found by Sean, and is already 
fixed in 5.8-rc4.

https://lore.kernel.org/kvm/20200605192605.7439-1-sean.j.christopherson@intel.com/