linux-kernel - Re: [tip:x86/mm] x86/boot/32: Defer resyncing initial_page

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Message-ID: <CAHp75VdX-kUqW0MKOSTz9zByU-eipBMnKpdUbTt2SVOJ8Kvrig@mail.gmail.com>
Date:   Mon, 8 May 2017 12:32:46 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>
Cc:     Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        x86 <x86@...nel.org>, linux-efi <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        jpoimboe@...hat.com, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brian Gerst <brgerst@...il.com>, thgarnie@...gle.com,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [tip:x86/mm] x86/boot/32: Defer resyncing initial_page_table
 until per-cpu is set up

On Mon, May 8, 2017 at 9:31 AM, Jan Kiszka <jan.kiszka@...mens.com> wrote:
> On 2017-03-23 10:14, tip-bot for Andy Lutomirski wrote:
>> The x86 smpboot trampoline expects initial_page_table to have the
>> GDT mapped.  If the GDT ends up in a virtually mapped per-cpu page,
>> then it won't be in the page tables at all until perc-pu areas are
>> set up.  The result will be a triple fault the first time that the
>> CPU attempts to access the GDT after LGDT loads the perc-pu GDT.
>>
>> This appears to be an old bug, but somehow the GDT fixmap rework
>> is triggering it.  This seems to have something to do with the
>> memory layout.

> This breaks the boot on our Intel Quark platform (IOT2000, similar to
> Galileo Gen2). Reverting it over master makes it work again. Any idea
> what goes wrong? Let me know how I can help debugging this.

JFYI: As of today linux-next when _kexec:ed_ works fine to me

Perhaps I can test this later with direct boot from SD card.

-- 
With Best Regards,
Andy Shevchenko