linux-kernel - Re: [tip:irq/numa] x86, apic: Fix dummy apic read operation together with broken MP handling

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Message-ID: <86802c440906071223w3116f452n7ccd028d52f11c77@mail.gmail.com>
Date:	Sun, 7 Jun 2009 12:23:47 -0700
From:	Yinghai Lu <yhlu.kernel@...il.com>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	gorcunov@...nvz.org, yinghai@...nel.org, tglx@...utronix.de,
	mingo@...e.hu
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:irq/numa] x86, apic: Fix dummy apic read operation together 
	with broken MP handling

On Sun, Jun 7, 2009 at 7:24 AM, tip-bot for Cyrill
Gorcunov<gorcunov@...nvz.org> wrote:
> Commit-ID:  103428e57be323c3c5545db8ad12667099bc6005
> Gitweb:     http://git.kernel.org/tip/103428e57be323c3c5545db8ad12667099bc6005
> Author:     Cyrill Gorcunov <gorcunov@...nvz.org>
> AuthorDate: Sun, 7 Jun 2009 16:48:40 +0400
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Sun, 7 Jun 2009 16:08:05 +0200
>
> x86, apic: Fix dummy apic read operation together with broken MP handling
>
> Ingo Molnar reported that read_apic is buggy novadays:
>
> [    0.000000] Using APIC driver default
> [    0.000000] SMP: Allowing 1 CPUs, 0 hotplug CPUs
> [    0.000000] Local APIC disabled by BIOS -- you can enable it with "lapic"
> [    0.000000] APIC: disable apic facility
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] WARNING: at arch/x86/kernel/apic/apic.c:254 native_apic_read_dummy+0x2d/0x3b()
> [    0.000000] Hardware name: HP OmniBook PC
>
> Indeed we still rely on apic->read operation for SMP compiled
> kernel. And instead of disfigure the SMP code with #ifdef we
> allow to call apic->read. To capture any unexpected results
> we check for apic->read being called for sane reason via
> WARN_ON_ONCE but(!) instead of OR we should use AND logical
> operation (thanks Yinghai for spotting the root of the problem).
>
> Along with that we could be have bad MP table and we are
> to fix it that way no SMP started and no complains about
> BIOS bug if apic was just disabled via command line.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> LKML-Reference: <20090607124840.GD4547@...ovo>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
>
>
> ---
>  arch/x86/kernel/apic/apic.c |    9 ++++++++-
>  arch/x86/kernel/smpboot.c   |    8 +++++---
>  2 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index e82488d..a4c9cf0 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -249,7 +249,7 @@ static void native_apic_write_dummy(u32 reg, u32 v)
>
>  static u32 native_apic_read_dummy(u32 reg)
>  {
> -       WARN_ON_ONCE((cpu_has_apic || !disable_apic));
> +       WARN_ON_ONCE((cpu_has_apic && !disable_apic));
>        return 0;
>  }
>
> @@ -1609,6 +1609,13 @@ void __init init_apic_mappings(void)
>        new_apicid = read_apic_id();
>        if (boot_cpu_physical_apicid != new_apicid) {
>                boot_cpu_physical_apicid = new_apicid;
> +               /*
> +                * yeah -- we lie about apic_version
> +                * in case if apic was disabled via boot option
> +                * but it's not a problem for SMP compiled kernel
> +                * since smp_sanity_check is prepared for such a case
> +                * and disable smp mode
> +                */
>                apic_version[new_apicid] =
>                         GET_APIC_VERSION(apic_read(APIC_LVR));
>        }
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index d2e8de9..7c80007 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -992,10 +992,12 @@ static int __init smp_sanity_check(unsigned max_cpus)
>         */
>        if (APIC_INTEGRATED(apic_version[boot_cpu_physical_apicid]) &&
>            !cpu_has_apic) {
> -               printk(KERN_ERR "BIOS bug, local APIC #%d not detected!...\n",
> -                       boot_cpu_physical_apicid);
> -               printk(KERN_ERR "... forcing use of dummy APIC emulation."
> +               if (!disable_apic) {
> +                       pr_err("BIOS bug, local APIC #%d not detected!...\n",
> +                               boot_cpu_physical_apicid);
> +                       pr_err("... forcing use of dummy APIC emulation."
>                                "(tell your hw vendor)\n");
> +               }

It seems we don't need this check here.
when we have disable_apic, cpu_has_apic is cleared forcely.

YH
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