From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 24 May 2004 21:39:05 -0700 (PDT) From: Linus Torvalds Subject: Re: [PATCH] ppc64: Fix possible race with set_pte on a present PTE In-Reply-To: <20040525042054.GU29378@dualathlon.random> Message-ID: References: <1085369393.15315.28.camel@gaston> <1085371988.15281.38.camel@gaston> <1085373839.14969.42.camel@gaston> <20040525034326.GT29378@dualathlon.random> <20040525042054.GU29378@dualathlon.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: Benjamin Herrenschmidt , Andrew Morton , Linux Kernel list , Ingo Molnar , Ben LaHaise , linux-mm@kvack.org, Architectures Group List-ID: On Tue, 25 May 2004, Andrea Arcangeli wrote: > On Mon, May 24, 2004 at 09:00:02PM -0700, Linus Torvalds wrote: > > > > > > On Tue, 25 May 2004, Andrea Arcangeli wrote: > > > > > > The below patch should fix it, the only problem is that it can screwup > > > some arch that might use page-faults to keep track of the accessed bit, > > > > Indeed. At least alpha does this - that's where this code came from. SO > > this will cause infinite page faults on alpha and any other "accessed bit > > in software" architectures. > > as you say the alpha has no accessed bit at all in hardware, so > it cannot generate page faults. It _does_ generate page faults. We do the accessed bit by clearing the "user readable" thing (or something. I forget the exact details, and I'm too lazy to check it out). And a page won't be _really_ readable until it has been marked young. If you don't mark it young, you'll get infinite page faults. That's how we do the accessed bit. > "accessed bit in software" is fine with my fix. NO IT IS NOT. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org