linux-kernel - Re: [PATCH 2/3] mm: page table check

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Date:   Tue, 30 Nov 2021 14:25:09 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Fusion Future <qydwhotmail@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Paul Turner <pjt@...gle.com>, weixugc@...gle.com,
        Greg Thelen <gthelen@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, masahiroy@...nel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE" <x86@...nel.org>,
        frederic@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH 2/3] mm: page table check

On Sun, Nov 28, 2021 at 9:57 PM Fusion Future <qydwhotmail@...il.com> wrote:
>
> On 2021/11/29 00:57, Pasha Tatashin wrote:
> > This commit by itself would not cause the freeze or BUG_ON(), but the
> > next commit which enables it on x86 arch might.
>
> Yes, you are right. At the commit
> "[1e67abff1820489435aad3fcf258708c21c283ef] x86: mm: add x86_64 support
> for page table check" my system starts to experience the freeze.
>
> I can now reproduce the freeze by following the steps below:
>
> 1. Open 20 YouTube video pages, and a YouTube Music page.
> 2. Play music in the background. (The step can be omitted)
> 3. Run `git clone
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git ln`

Thanks, I found a reliable way to reproduce this problem on my workstation:
reduce the amount of physical memory to 4G via memmap kernel
parameter,  and use a script that starts chrome browser with 20 tabs
each pointing to a youtube.com page.

I will send an update after root cause.

> git will never successfully clone the repo because the system will
> freeze during the operation.
>
> I also tried adding `page_table_check=off` to the boot option but still

I will add support for page_table_check=off even when
CONFIG_PAGE_TABLE_CHECK_ENFORCED is set

Thanks,
Pasha