From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965119AbbJHR3E (ORCPT ); Thu, 8 Oct 2015 13:29:04 -0400 Received: from foss.arm.com ([217.140.101.70]:35687 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965137AbbJHR3B (ORCPT ); Thu, 8 Oct 2015 13:29:01 -0400 Date: Thu, 8 Oct 2015 18:28:56 +0100 From: Catalin Marinas To: "Suzuki K. Poulose" Cc: Christoffer Dall , Marc Zyngier , kvm@vger.kernel.org, ard.biesheuvel@linaro.org, Will Deacon , linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 03/15] arm64: Introduce helpers for page table levels Message-ID: <20151008172856.GQ17192@e104818-lin.cambridge.arm.com> References: <1442331684-28818-1-git-send-email-suzuki.poulose@arm.com> <1442331684-28818-4-git-send-email-suzuki.poulose@arm.com> <20151007082652.GM9011@cbox> <5614E536.9040007@arm.com> <20151008144546.GD20936@cbox> <5616A65A.50003@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5616A65A.50003@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 08, 2015 at 06:22:34PM +0100, Suzuki K. Poulose wrote: > On 08/10/15 15:45, Christoffer Dall wrote: > >On Wed, Oct 07, 2015 at 10:26:14AM +0100, Marc Zyngier wrote: > >>I just had a chat with Catalin, who did shed some light on this. > >>It all has to do with rounding up. What you would like to have here is: > >> > >>#define ARM64_HW_PGTABLE_LEVELS(va_bits) DIV_ROUND_UP(va_bits - PAGE_SHIFT, PAGE_SHIFT - 3) > >> > >>where (va_bits - PAGE_SHIFT) is the total number of bits we deal > >>with during a page table walk, and (PAGE_SHIFT - 3) is the number > >>of bits we deal with per level. > >> > >>The clue is in how DIV_ROUND_UP is written: > >> > >>#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) > >> > >>which gives you Suzuki's magic formula. > >> > >>I'd vote for the DIV_ROUND_UP(), which will make things a lot more readable. > >> > >Thanks for the explanation, I vote for DIV_ROUND_UP too. > > Btw, DIV_ROUND_UP is defined in linux/kernel.h, including which in the required > headers breaks the build. I could add the definition of the same locally. Or just keep the original magic formula and add the DIV_ROUND_UP one in a comment. -- Catalin