linux-kernel - Re: [PATCH] x86: don't map io

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Message-ID: <86802c440905200103o5905e997weec5da0fd0a86c41@mail.gmail.com>
Date:	Wed, 20 May 2009 01:03:14 -0700
From:	Yinghai Lu <yhlu.kernel@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: don't map io_apic two times.

On Wed, May 20, 2009 at 12:58 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Yinghai Lu <yinghai@...nel.org> wrote:
>
>> mp_register_ioapic() already map it.
>>
>> [ Impact: don't map io apic address again ]
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>>
>> ---
>>  arch/x86/kernel/apic/io_apic.c |    7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
>> ===================================================================
>> --- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
>> +++ linux-2.6/arch/x86/kernel/apic/io_apic.c
>> @@ -4162,7 +4162,12 @@ fake_ioapic_page:
>>                               alloc_bootmem_pages(PAGE_SIZE);
>>                       ioapic_phys = __pa(ioapic_phys);
>>               }
>> -             set_fixmap_nocache(idx, ioapic_phys);
>> +             /*
>> +              * when acpi ioapic is used, mp_register_ioapic() map
>> +              * ioapic_phys already
>> +              */
>> +             if (!acpi_ioapic)
>> +                     set_fixmap_nocache(idx, ioapic_phys);
>
> The change is correct, but i'm not sure we want to do this - the
> acpi_ioapic flag might change its meaning (and then break this code
> subtly) and this is bootup code so doing the mapping twice should be
> no issue.
>
> If it were some expensive initialization i'd agree, but here it's
> really just a couple of instructions and an INVLPG.
>
> Hm?

ok, please drop it.

YH
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