linux-kernel - Re: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE

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Message-ID: <20150305003417.GC20449@gmail.com>
Date:	Thu, 5 Mar 2015 01:34:17 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...capital.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE_2


* Borislav Petkov <bp@...en8.de> wrote:

> On Wed, Mar 04, 2015 at 08:13:24AM +0100, Ingo Molnar wrote:
> > Btw., the x86 memset() variants are using this today, and I think this 
> > is the most optimal jump-patching variant, even if it means a small 
> > amount of code duplication between the copy_user variants.
> 
> Yeah, the problem with that one was that we patch a huge amount of code,
> see the dump below.
> 
> The X86_FEATURE_REP_GOOD thing replaces a 172 bytes memset with the 
> 42 byte REP;STOSQ version and the X86_FEATURE_ERMS does the same 
> with REP;STOSB.

So I'd not patch in the large _orig variant, it's legacy mostly - but 
the two fast variants?

Thanks,

	Ingo
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