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SubjectRe: [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
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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?

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.

If anyone is encountering real issues, please speak up.

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