linux-kernel - Re: [PATCH 13/17] x86-64: Remove pda

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Message-ID: <73c1f2160901172120i174a8933qfdb51e654f13c785@mail.gmail.com>
Date:	Sun, 18 Jan 2009 00:20:45 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] x86-64: Remove pda_init()

On Sat, Jan 17, 2009 at 11:32 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> Brian Gerst wrote:
>> -void __cpuinit pda_init(int cpu)
>> -{
>> -     struct x8664_pda *pda = cpu_pda(cpu);
>> -
>> -     /* Setup up data that may be needed in __get_free_pages early */
>> -     loadsegment(fs, 0);
>> -     loadsegment(gs, 0);
>> -
>> -     load_pda_offset(cpu);
>> -}
>
> Simply removing these should work fine as they're also initialized in
> other places earlier but I think they still need to be in cpu_init()
> because...
>
> /*
>  * cpu_init() initializes state that is per-CPU. Some data is already
>  * initialized (naturally) in the bootstrap process, such as the GDT
>  * and IDT. We reload them nevertheless, this function acts as a
>            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>  * 'CPU state barrier', nothing should get across.
>  * A lot of state is already set up in PDA init for 64 bit
>  */

That comment seems like overkill.  It may have been relevant in an
earlier time, but I don't think we need to be so strict now,
especially for things we know are set properly in head_xx.S.

--
Brian Gerst
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