From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id B45856B0055 for ; Sun, 31 May 2009 02:13:52 -0400 (EDT) Received: by bwz21 with SMTP id 21so9272815bwz.38 for ; Sat, 30 May 2009 23:14:03 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20090531001052.40ac57d2@lxorguk.ukuu.org.uk> References: <20090528090836.GB6715@elte.hu> <20090530082048.GM29711@oblivion.subreption.com> <20090530173428.GA20013@elte.hu> <20090530180333.GH6535@oblivion.subreption.com> <20090530182113.GA25237@elte.hu> <20090530184534.GJ6535@oblivion.subreption.com> <20090530190828.GA31199@elte.hu> <4A21999E.5050606@redhat.com> <84144f020905301353y2f8c232na4c5f9dfb740eec4@mail.gmail.com> <20090531001052.40ac57d2@lxorguk.ukuu.org.uk> Date: Sun, 31 May 2009 09:14:03 +0300 Message-ID: <84144f020905302314w12c4c7f8jc8241e36c847f53e@mail.gmail.com> Subject: Re: [patch 0/5] Support for sanitization flag in low-level page allocator From: Pekka Enberg Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Alan Cox Cc: Rik van Riel , Ingo Molnar , "Larry H." , linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org, Ingo Molnar , pageexec@freemail.hu, Linus Torvalds List-ID: Hi Alan, On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: >> It's pretty damn obvious that Larry's patches have a much bigger >> performance impact than using kzfree() for selected parts of the >> kernel. So yes, I do expect him to benchmark and demonstrate that >> kzfree() has _performance problems_ before we can look into merging >> his patches. > > We seem to be muddling up multiple things here which is not helpful. Yup. On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: > There are three things going on > > #1 Is ksize() buggy ? No, there's nothing wrong with ksize() I am aware of. Yes, Larry has been saying it is but hasn't provided any evidence so far. On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: > #2 Using kzfree() to clear specific bits of memory (and I question the > kzfree implementation as it seems ksize can return numbers much much > bigger than the allocated space you need to clear - correct but oversize) > or using other flags. I'd favour kzfree personally (and fixing it to work > properly) Well, yes, that's what kzfree() needs to do given the current API. I am not sure why you think it's a problem, though. Adding a size argument to the function will make it more error prone. On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: > #3 People wanting to be able to select for more security *irrespective* > of performance cost. Which is no different to SELinux for example. Yeah, as I said before, I really don't have any objections to this. I just think nobody is going to enable it so memset() or kzfree() in relevant places is probably a good idea. Pekka -- 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: email@kvack.org