linux-kernel - Re: [patch 1/2] x86_64 page fault NMI-safe

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Message-ID: <AANLkTin8JxUJkltswhmkMMThZmc6HceURCyMXnqlhbT0@mail.gmail.com>
Date:	Thu, 15 Jul 2010 08:38:51 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <rostedt@...tedt.homelinux.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>, Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Tejun Heo <htejun@...il.com>
Subject: Re: [patch 1/2] x86_64 page fault NMI-safe

On Thu, Jul 15, 2010 at 7:51 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So it's not the lazy page table fill that is the problem. Never has
> been. We've been doing the lazy fill for a long time, and it was
> simple and useful way back when.

Btw, this is true to the degree that I would _much_ rather just get
rid of the crazy "vmalloc_sync_all()" crap entirely, and make it clear
that non-lazy vmalloc page table fill is a bug.

Because quite frankly, it _is_ a bug to depend on non-lazy vmalloc.
The whole function is only implemented on 32-bit x86, so any code that
thinks it needs it is either just wrong, or will only work on 32-bit
x86 anyway (and on other architectures by pure chance, likely because
their VM fill granularity is so big that they never saw the problem).

So getting rid of vmalloc_sync_all() entirely would be a good thing.
Then we wouldn't have that silly and pointless interface, and we
wouldn't have that crazy "this only does something on x86-32,
everywhere else it's a placebo".

                      Linus
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