linux-kernel - Re: [patch 8/9] F00F bug fixup for i386

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Message-Id: <20070531174355.544e7588.akpm@linux-foundation.org>
Date:	Thu, 31 May 2007 17:43:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	mathieu.desnoyers@...ymtl.ca, linux-kernel@...r.kernel.org
Subject: Re: [patch 8/9] F00F bug fixup for i386 - use conditional calls

On Fri, 1 Jun 2007 02:14:53 +0200 (MEST)
Mikael Pettersson <mikpe@...uu.se> wrote:

> Andrew Morton wrote:
> > Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> > 
> > > * Andrew Morton (akpm@...ux-foundation.org) wrote:
> > >  
> > > > > Use the faster conditional calls for F00F bug handling in do_page_fault.
> > > > > 
> > > > 
> > > > I guess this means that CONDCALL will be enabled on pretty much all i386,
> > > > in which case making the whole feature Kconfigurable is starting to look
> > > > marginal.
> > > > 
> > > > Perhaps a better approach would have to made this change dependent upon
> > > > CONDCALL, rather than forcing it on.
> > > > 
> > > 
> > > Do you mean making X86_F00F_BUG depend on COND_CALL instead of selecting
> > > it ?
> > 
> > yup
> 
> X86_F00F_BUG needs to be enabled in all kernels capable of booting on
> P5 class machines, whether or not some obscure CONFIG_COND_CALL thingy
> is enabled or not. X86_F00F_BUG is not some optional optimisation, it's
> an essential workaround for a serious hardware bug.
> 
> Therefore it seems select rather than depend is called for.

Nope.

CONFIG_COND_CALL=n	-> 	do f00f handling the present way
CONFIG_COND_CALL=y	-> 	do f00f handling the new, fast-n-fancy way


Because I don't think everyone will want to drag all this cond_call stuff
into their kernel just for slightly faster f00f handling.

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