linux-kernel - Re: [RFC PATCH] Drop some asm from copy_user

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Message-ID: <20150513104630.GA7751@gmail.com>
Date:	Wed, 13 May 2015 12:46:30 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Drop some asm from copy_user_64.S


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

> On Wed, May 13, 2015 at 12:31:40PM +0200, Ingo Molnar wrote:
> > So why should an alternatives-CALL, inlined directly into call sites,
> > cost more kernel space?
> 
> Not the alternatives CALL alone but inlining _copy_*_user with all 
> the preparation glue around it would. Basically what we're doing 
> currently.

So I reacted to this comment of yours:

> > > The disadvantage is that we have CALL after CALL [...]

Is the CALL after CALL caused by us calling an alternatives patched 
function? If yes then we probably should not do that: alternatives 
switching should IMHO happen at the highest possible level.

Thanks,

	Ingo
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