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

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Message-Id: <20070531142138.60dbc8a9.akpm@linux-foundation.org>
Date:	Thu, 31 May 2007 14:21:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 8/9] F00F bug fixup for i386 - use conditional calls

On Thu, 31 May 2007 17:07:55 -0400
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

> > > +	if (cond_call(fix_f00f, do_f00f_workaround(regs, address)))
> > > +		return;
> > 
> > We do a cond_call() to an inlined function?  That's a bit weird, isn't it?
> > 
> 
> Yes, but it works :) I will add this information to the documentation.

But why does it work?  Did the compiler generate an out-of-line copy
of the function?  If so, we'll end up with multiple copies of the function if
there are other callers.  If not, the `inline' was pointless.
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