linux-kernel - Re: [lkp-robot] [x86] 69218e4799: BUG:kernel_hang_in_boot

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Message-ID: <20170322073608.GA5538@gmail.com>
Date:   Wed, 22 Mar 2017 08:36:08 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Garnier <thgarnie@...gle.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel test robot <xiaolong.ye@...el.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...e.de>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Jiri Kosina <jikos@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Jonathan Corbet <corbet@....net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Len Brown <len.brown@...el.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Michal Hocko <mhocko@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        zijun_hu <zijun_hu@....com>, LKML <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, LKP <lkp@...org>
Subject: Re: [lkp-robot] [x86] 69218e4799: BUG:kernel_hang_in_boot_stage


* Thomas Garnier <thgarnie@...gle.com> wrote:

> >  static inline void setup_fixmap_gdt(int cpu)
> >  {
> >         __set_fixmap(get_cpu_gdt_ro_index(cpu),
> > -                    __pa(get_cpu_gdt_rw(cpu)), pg_fixmap_gdt_flags);
> > +                    slow_virt_to_phys(get_cpu_gdt_rw(cpu)),
> > +                    pg_fixmap_gdt_flags);
> >  }
> >
> >  /* Load the original GDT from the per-cpu structure */
> >
> > This makes UP boot for me, but SMP (2 cpus) is still busted.
> 
> This change fixed boot for me:
> 
> diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
> index b65155cc3760..4e30707d9f9a 100644
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -104,7 +104,9 @@ enum fixed_addresses {
>         FIX_GDT_REMAP_BEGIN,
>         FIX_GDT_REMAP_END = FIX_GDT_REMAP_BEGIN + NR_CPUS - 1,
> 
> -       __end_of_permanent_fixed_addresses,
> +       __end_of_permanent_fixed_addresses =
> +               (FIX_GDT_REMAP_END + PTRS_PER_PTE - 1) &
> +               -PTRS_PER_PTE,
> 
> Just ensure PKMAP_BASE & FIX_WP_TEST are on a different PMD.
> 
> I don't think that the right fix but it might help understand the
> exact root cause.

Could this be related to the permission bits in the PMD itself getting out of sync 
with the PTEs? WP test marks a page writable/unwritable, and maybe we mess up the 
restoration. If they are on separate PMDs then this is worked around because the 
fixmap GDT is on a separate PMD.

Thanks,

	Ingo