linux-kernel - Re: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys

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Date:	Tue, 5 Feb 2013 08:53:05 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Stoney Wang <song-bo.wang@...com>, stable@...nel.org
Subject: Re: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe()

On Tue, Feb 5, 2013 at 4:24 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Yinghai Lu <yinghai@...nel.org> wrote:
>
>> From: Stoney Wang <song-bo.wang@...com>
>>
>> When HP ProLiant DL980 G7 Server boot without x2apic_phys, there will be
>> intermittent lost interrupts and could result in a hang or data loss.
>
> What does 'boot without x2apic_phys' mean?
>
> Does it mean x2apic_phys=0 boot command line? Or, because
> x2apic_phys is off by default, does it simply mean that if it's
> booted with a default kernel, without any workaround specified
> on the boot command line?

means that user does not append "x2apic_phys" in boot command line.

current we have:

        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
                        default x2apic cluster mode on platforms
                        supporting x2apic.

int x2apic_phys;

static int set_x2apic_phys_mode(char *arg)
{
        x2apic_phys = 1;
        return 0;
}
early_param("x2apic_phys", set_x2apic_phys_mode);

if the user specify "x2apic_phys=0", kernel still enable x2apic_phys.

Now because system could enable x2apic phys mode via fadt, do we
need to make "x2apic_phys=0" works as disabling x2apic_phys and
overriding FADT ?

Thanks

Yinghai
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