linux-kernel - Re: [tip:x86/mm] x86: Convert the rest of the code to support p4d

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Date:   Mon, 24 Apr 2017 11:42:34 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     dvlasenk@...hat.com, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, brgerst@...il.com,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86: Convert the rest of the code to support p4d_t

On Mon, Apr 24, 2017 at 9:57 AM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
> On Sun, Apr 23, 2017 at 12:56:14PM -0700, Dan Williams wrote:
>> On Mon, Mar 27, 2017 at 3:25 AM, tip-bot for Kirill A. Shutemov
>> <tipbot@...or.com> wrote:
>> > Commit-ID:  f2a6a7050109e0a5c7a84c70aa6010f682b2f1ee
>> > Gitweb:     http://git.kernel.org/tip/f2a6a7050109e0a5c7a84c70aa6010f682b2f1ee
>> > Author:     Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> > AuthorDate: Fri, 17 Mar 2017 21:55:15 +0300
>> > Committer:  Ingo Molnar <mingo@...nel.org>
>> > CommitDate: Mon, 27 Mar 2017 08:56:58 +0200
>> >
>> > x86: Convert the rest of the code to support p4d_t
>> >
>> > This patch converts x86 to use proper folding of a new (fifth) page table level
>> > with <asm-generic/pgtable-nop4d.h>.
>> >
>> > That's a bit of a kitchen sink patch, but I don't see how to split it further
>> > without hurting bisectability.
>> >
>> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> > Acked-by: Thomas Gleixner <tglx@...utronix.de>
>> > Cc: Andrew Morton <akpm@...ux-foundation.org>
>> > Cc: Andy Lutomirski <luto@...capital.net>
>> > Cc: Andy Lutomirski <luto@...nel.org>
>> > Cc: Arnd Bergmann <arnd@...db.de>
>> > Cc: Borislav Petkov <bp@...en8.de>
>> > Cc: Brian Gerst <brgerst@...il.com>
>> > Cc: Dave Hansen <dave.hansen@...el.com>
>> > Cc: Denys Vlasenko <dvlasenk@...hat.com>
>> > Cc: H. Peter Anvin <hpa@...or.com>
>> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
>> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> > Cc: Michal Hocko <mhocko@...e.com>
>> > Cc: Peter Zijlstra <peterz@...radead.org>
>> > Cc: linux-arch@...r.kernel.org
>> > Cc: linux-mm@...ck.org
>> > Link: http://lkml.kernel.org/r/20170317185515.8636-7-kirill.shutemov@linux.intel.com
>> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
>>
>> Following Ingo's revert of commit 2947ba054a4d "x86/mm/gup: Switch GUP
>> to the generic get_user_page_fast() implementation", I gave
>> tip.git/master a try to see if it resolved the original failing
>> signature I was seeing with the "device-dax" regression test [1] on
>> next/master. It turns out that there are two failing signatures and I
>> need to use the revert during the bisect to find this other
>> regression. This new bisect points to commit f2a6a7050109 "x86:
>> Convert the rest of the code to support p4d_t" as the culprit.
>>
>> [   43.194330] BUG: unable to handle kernel paging request at ffff880300000000
>
> I cannot reproduce the issue.
>
> Could you share your kernel kernel config?

Kernel config available here:
https://gist.github.com/djbw/2b99a014396cca9f4406586573be98c0