linux-kernel - Re: [Stable-review] [12/28] x86, cpu: Clean up AMD erratum 400 workaround

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Date:	Wed, 20 Apr 2011 05:48:30 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg KH <gregkh@...e.de>
Cc:	Hans Rosenfeld <hans.rosenfeld@....com>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	akpm@...ux-foundation.org, "H. Peter Anvin" <hpa@...ux.intel.com>,
	torvalds@...ux-foundation.org, stable-review@...nel.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [Stable-review] [12/28] x86, cpu: Clean up AMD erratum 400
 workaround

On Tue, 2011-04-19 at 20:11 -0700, Greg KH wrote:
> On Wed, Apr 20, 2011 at 03:17:42AM +0100, Ben Hutchings wrote:
> > On Tue, 2011-04-19 at 19:01 -0700, Greg KH wrote:
> > > On Wed, Apr 20, 2011 at 02:40:53AM +0100, Ben Hutchings wrote:
> > > > On Tue, 2011-04-19 at 13:30 -0700, Greg KH wrote:
> > > > > 2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> > > > > 
> > > > > ------------------
> > > > > 
> > > > > From: Hans Rosenfeld <hans.rosenfeld@....com>
> > > > > 
> > > > > commit 9d8888c2a214aece2494a49e699a097c2ba9498b upstream.
> > > > > 
> > > > > Remove check_c1e_idle() and use the new AMD errata checking framework
> > > > > instead.
> > > > 
> > > > Clean-up patches are generally not candidates for longterm updates.
> > > 
> > > This was added because a follow-on patch required it.
> > 
> > Ah yes, 'x86, AMD: Set ARAT feature on AMD processors' is using the same
> > condition.
> > 
> > Of course, that could have been backported by referring to the function
> > that this removes, rather than pulling in a load of other changes with
> > consequent risk of regressions.
> 
> I prefer to take original patches for stable, it makes it easier in the
> end.

It makes what easier, when?  What I see here is a bug fix that is much
larger than necessary, with a consequent risk of regression that seems
way out of proportion to the benefit.  (What actually *is* the benefit
of these AMD changes?)  And we have had several serious regressions in
the 2.6.32.y series recently, so I really don't think we are getting the
trade-off right.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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