linux-kernel - Re: [RFC PATCH 1/9] uaccess: Make copy_from_user

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Date:	Wed, 13 Oct 2010 09:15:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Robert Richter <robert.richter@....com>
Subject: Re: [RFC PATCH 1/9] uaccess: Make copy_from_user_nmi() globally
 available

On Wed, 2010-10-13 at 07:06 +0200, Frederic Weisbecker wrote:
> In order to support user stack dump safely in perf samples from
> generic code, export copy_from_user_nmi() from x86 and make it
> generally available. For most archs it will map to
> copy_from_user_inatomic, but for x86 we need to take care of
> not faulting from NMIs.
> 
> Since perf is the first user for now, let the overriden x86
> implementation in the perf source file.

It might make sense to call it copy_from_user_gup() because that's
bascially what it does, it doesn't rely on NMI context anymore, its just
NMI-safe.

Its a best effort software page table walk, and with the stacked
kmap_atomic bits Andrew took it should work from any context.


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