linux-kernel - Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb

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Date:	Thu, 17 May 2012 13:28:06 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Russell King <rmk@....linux.org.uk>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Chris Metcalf <cmetcalf@...era.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb

On Thu, 2012-05-17 at 10:51 +0100, Russell King wrote:
> On Thu, May 17, 2012 at 10:30:23AM +0100, Catalin Marinas wrote:
> > Another minor thing is that on newer ARM processors (Cortex-A15) we
> > need the TLB shootdown even on UP systems, so tlb_fast_mode should
> > always return 0. Something like below (untested):
> 
> No Catalin, we need this for virtually all ARMv7 CPUs whether they're UP
> or SMP, not just for A15, because of the speculative prefetch which can
> re-load TLB entries from the page tables at _any_ time.

Hmm,. so this is mostly because of the confusion/coupling between
tlb_remove_page() and tlb_remove_table() I guess. Since I don't see the
freeing of the actual pages being a problem with speculative TLB
reloads, just the page-tables.

Should we introduce a tlb_remove_table() regardless of
HAVE_RCU_TABLE_FREE which always queues the tables regardless of
tlb_fast_mode()? 


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