Re: kvm crash on 5.7-rc1 and later

[Woody Suwalski <terraluna977@gmail.com>]

Woody Suwalski wrote:
> Xiaoyao Li wrote:
>> 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/ 
>>
>
> You are right, kvm works OK on 5.8-rc4.
> The fix will need to be backported to 5.7.
>
> Thanks, Woody
>
I see it is already in 5.7.8. Great :-)
Thanks, Woody