From: Andi Kleen <ak@suse.de>
To: Zoltan Menyhart <Zoltan.Menyhart@bull.net>
Cc: linux-mm@kvack.org, Zoltan.Menyhart@free.fr
Subject: Re: RFC: RCU protected page table walking
Date: Wed, 3 May 2006 18:46:51 +0200 [thread overview]
Message-ID: <200605031846.51657.ak@suse.de> (raw)
In-Reply-To: <4458CCDC.5060607@bull.net>
s page table walking is not atomic, not even on an x86.
>
> Let's consider the following scenario:
>
>
> CPU #1: CPU #2: CPU #3
>
> Starts walking
> Got the ph. addr. of page Y
> in internal reg. X
> free_pgtables():
> sets free page Y
The page is not freed until all CPUs who had the mm mapped are flushed.
See mmu_gather in asm-generic/tlb.h
> Allocates page Y
> Accesses page Y via reg. X
>
>
> As CPU #1 is still keeping the same ph. address, it fetches an item
> from a page that is no more its page.
>
> Even if this security window is small, it does exist.
It doesn't at least on architectures that use the generic tlbflush.h
-Andi
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next prev parent reply other threads:[~2006-05-03 16:46 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-03 15:31 RFC: RCU protected page table walking Zoltan Menyhart
2006-05-03 16:46 ` Andi Kleen [this message]
2006-05-03 18:00 ` Hugh Dickins
2006-05-03 23:54 ` Christoph Lameter
2006-05-03 23:54 ` Christoph Lameter
2006-05-04 2:51 ` Chen, Kenneth W
2006-05-04 4:28 ` Hugh Dickins
2006-05-04 9:26 ` Zoltan Menyhart
2006-05-04 9:31 ` Andi Kleen
2006-05-04 11:32 ` Zoltan Menyhart
2006-05-04 12:00 ` Andi Kleen
2006-05-04 13:13 ` Robin Holt
2006-05-04 13:54 ` Zoltan Menyhart
2006-05-04 15:27 ` Hugh Dickins
2006-05-04 15:27 ` Hugh Dickins
2006-05-04 9:19 ` Zoltan Menyhart
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