linux-kernel - Re: [lkp-robot] [bisect done] e71e836f46 [ 17.567570] WARNING: CPU: 0 PID: 1 at arch/x86/include/asm/pgtable.h:540 __change_page_attr_set

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Date:   Wed, 11 Apr 2018 08:35:53 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     kernel test robot <lkp@...el.com>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org, LKP <lkp@...org>
Subject: Re: [lkp-robot] [bisect done] e71e836f46 [ 17.567570] WARNING: CPU:
 0 PID: 1 at arch/x86/include/asm/pgtable.h:540 __change_page_attr_set_clr

Hi Dave,

On Tue, Apr 10, 2018 at 01:59:21PM -0700, Dave Hansen wrote:
>On 04/09/2018 06:12 PM, kernel test robot wrote:
>> +-----------------------------------------------------------------------+------------+------------+------------+------------+
>> |                                                                       | 64c8075940 | e71e836f46 | 0564258fb2 | 87e1e2f51c |
>> +-----------------------------------------------------------------------+------------+------------+------------+------------+
>> | boot_successes                                                        | 35         | 0          | 19         | 11         |
>> | boot_failures                                                         | 0          | 26         |            |            |
>> | WARNING:at_arch/x86/include/asm/pgtable.h:#__change_page_attr_set_clr | 0          | 26         |            |            |
>> | RIP:__change_page_attr_set_clr                                        | 0          | 26         |            |            |
>> +-----------------------------------------------------------------------+------------+------------+------------+------------+
>
>LKP folks, does this mean that the system didn't boot in all the places
>that we saw this warning?  Or does this just say that it *had* the
>warning 26 times?

The 'e71e836f46' column means there are 0 boots (sorry boot_successes
might be a bit confusing) with clean dmesg and 26 boots with
warning/error dmesg. It indicates that WARNING is 100% reproducible.

        boot_successes + boot_failures = total test boots

>I looked into this a bit.  This LKP report points the finger at this
>commit which trips over a new debugging WARN_ON() I added:
>
>[patch 06/11] x86/mm: Remove extra filtering in pageattr code
>
>It's because set_memory_nx() encounters the (unsupported) _PAGE_GLOBAL
>bit while clearing _PAGE_NX.  I never saw this in testing because this
>patch:
>
>[PATCH 10/11] x86/pti: never implicitly clear _PAGE_GLOBAL for kernel image
>
>explicitly clears out _PAGE_GLOBAL long before the set_memory_nx() call.
>So I *think* this is a transient issue resulting in bad ordering of the
>_PAGE_GLOBAL patch set.  I believe it is harmless.

Right. The '0564258fb2' and '87e1e2f51c' columns mean the
'tip/x86/pti' and 'tip/master' branch HEADs boot clean.
So it's a transient warning inside the branch.

Thanks,
Fengguang