linux-kernel - Re: [PATCH v8 07/10] x86, mpx: decode MPX instruction to get bound violation information

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Message-ID: <alpine.DEB.2.10.1409120133330.4178@nanos>
Date:	Fri, 12 Sep 2014 01:37:10 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Dave Hansen <dave.hansen@...el.com>,
	Qiaowei Ren <qiaowei.ren@...el.com>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 07/10] x86, mpx: decode MPX instruction to get bound
 violation information

On Thu, 11 Sep 2014, H. Peter Anvin wrote:

> On 09/11/2014 03:32 PM, Dave Hansen wrote:
> > On 09/11/2014 03:18 PM, Thomas Gleixner wrote:
> >> On Thu, 11 Sep 2014, Qiaowei Ren wrote:
> >>> This patch sets bound violation fields of siginfo struct in #BR
> >>> exception handler by decoding the user instruction and constructing
> >>> the faulting pointer.
> >>>
> >>> This patch does't use the generic decoder, and implements a limited
> >>> special-purpose decoder to decode MPX instructions, simply because the
> >>> generic decoder is very heavyweight not just in terms of performance
> >>> but in terms of interface -- because it has to.
> >>
> >> And why is that an argument to add another special purpose decoder?
> > 
> > Peter asked for it to be done this way specifically:
> > 
> > 	https://lkml.org/lkml/2014/6/19/411
> > 
> 
> Specifically because marshaling the data in and out of the generic
> decoder was more complex than a special-purpose decoder.

I did not look at that detail and I trust your judgement here, but
that is in no way explained in the changelog.

This whole patchset is a pain to review due to half baken changelogs
and complete lack of a proper design description.

Thanks,

	tglx
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