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

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Message-ID: <1303356555.3464.128.camel@localhost>
Date:	Thu, 21 Apr 2011 04:29:15 +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 22:06 -0700, Greg KH wrote:
> On Wed, Apr 20, 2011 at 05:48:30AM +0100, Ben Hutchings wrote:
> > 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.
> 
> We got a few new quirks added for AMD hardware platforms that fix
> problems.

Maybe, but I still haven't seen anyone explain what those problems are!

> It took 3 patches to get there, yes, but now, as time goes
> on, adding new ones is even easier as the .32 code matches the .39 code
> in this area due to these patches being added.
> 
> Now if you find problems in these, great, let me know and I will work to
> resolve them.
> 
> As for regressions, what are you referring to?

These are the regressions I'm aware of in the last few updates:

2.6.32.36: 'x86: Cleanup highmap after brk is concluded' broke
hibernation on x86-64 and some x86-32 machines (reverted in .37)
2.6.32.36: 'signal: Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from
spoofing the signal code' broke glibc aio (fixed in .37)
2.6.32.34: powerpc kdump/kexec changes didn't compile on UP or 32-bit
(fixed in .37)
2.6.32.30: 'x86 quirk: Fix polarity for IRQ0 pin2 override on SB800
systems' broke the revision check for other quirks (fixed in .34)
2.6.32.29: 'USB: Prevent buggy hubs from crashing the USB stack' broke
MUSB on BeagleBoards (still unfixed?)
 
Ben.

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

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