Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755686Ab2JVQL6 (ORCPT ); Mon, 22 Oct 2012 12:11:58 -0400 Received: from one.firstfloor.org ([213.235.205.2]:58996 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755545Ab2JVQL5 (ORCPT ); Mon, 22 Oct 2012 12:11:57 -0400 Date: Mon, 22 Oct 2012 18:11:51 +0200 From: Andi Kleen To: "Michael Kerrisk (man-pages)" Cc: Andi Kleen , Andi Kleen , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hillf Danton Subject: Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Message-ID: <20121022161151.GS16230@one.firstfloor.org> References: <1350665289-7288-1-git-send-email-andi@firstfloor.org> <20121022132733.GQ16230@one.firstfloor.org> <20121022133534.GR16230@one.firstfloor.org> <20121022153633.GK2095@tassilo.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1964 Lines: 51 On Mon, Oct 22, 2012 at 05:53:45PM +0200, Michael Kerrisk (man-pages) wrote: > I'm not sure whether anything is using the high 8 bits of prot, bun > passing I note that there seems to be no check that the unused bits > are zeroed so there's a small chance existing apps are passing random > garbage there. (Of course, mmap() is hardly the only API to have that > fault, and it hasn't stopped us from reusing bits in those APIs, > though sometimes we've gotten bitten by apps that did pass in random > garbage). Ok. > > >> But there seems an obvious solution here: given your value in those > >> bits (call it 'n'), the why not apply a multiplier. I mean, certainly > >> you never want a value <= 12 for n, and I suspect that the reasonable > >> minimum could be much larger (e.g., 2^16). Call that minimum M. Then > >> you could interpret the value in your bits as meaning a page size of > >> > >> (2^n) * M > > > > I considered that, but it would seem ugly and does not add that > > many bits. > > > >> > >> > So this will use up all remaining flag bits now. > >> > >> On the other hand, that seems really bad. It looks like that kills the > >> ability to further extend the mmap() API with new flags in the future. > >> It doesn't sound like we should be doing that. > > > > You can always add flags to PROT or add a mmap3(). Has been done before. > > Or just don't do any new MAP_SECURITY_HOLEs > > There seems to be a reasonable argument here for an mmap3() with a > 64-bit flags argument... It's just a pain to deploy. I think I would rather do the offset then. That could still handle PowerPC 14 + 31 = 44 = 16GB (minimum size 16K) -Andi -- ak@linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/