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Date:	Thu, 19 Jun 2014 10:32:45 -0700
From:	"H. Peter Anvin" <>
To:	Dave Hansen <>,
	"Ren, Qiaowei" <>,
	Borislav Petkov <>
CC:	Thomas Gleixner <>,
	Ingo Molnar <>,
	"" <>,
	"" <>
Subject: Re: [PATCH v6 07/10] x86, mpx: decode MPX instruction to get bound
 violation information

On 06/19/2014 10:04 AM, Dave Hansen wrote:
> Could you please support this position with some data?  I'm a bit
> skeptical that instruction decoding is going to be a
> performance-critical path.
> I also don't see the extra field that you talked about in the previous
> thread?  What's the extra field?  I see a 'limit' vs. 'length', but you
> don't use 'length' at all, so I think you can use it instead, or at
> least union it.
> I've taken a quick stab at trying to consolidate things.  I think I may
> have screwed up this:
> 	insn->limit = MAX_MPX_INSN_SIZE - bytes;
> Qiaowei, is there anything fundamentally broken with what I've got here?

So I encouraged Qiaowei to do a limited special-purpose decoder, simply
because the glue to use the generic decoder was almost as large.  I am
overall not a huge fan of using the generic decoder in constrained
situation, because the generic decoder is very heavyweight not just in
terms of performance but in terms of interface -- because it has to.


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