From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753786AbbJNRII (ORCPT ); Wed, 14 Oct 2015 13:08:08 -0400 Received: from foss.arm.com ([217.140.101.70]:59711 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752522AbbJNRIE (ORCPT ); Wed, 14 Oct 2015 13:08:04 -0400 Date: Wed, 14 Oct 2015 18:07:59 +0100 From: Mark Rutland To: "Suzuki K. Poulose" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will.deacon@arm.com, steve.capper@linaro.org, marc.zyngier@arm.com, ard.biesheuvel@linaro.org, christoffer.dall@linaro.org Subject: Re: [PATCHv3 03/11] arm64: Introduce helpers for page table levels Message-ID: <20151014170759.GE5041@leverpostej> References: <1444821634-1689-1-git-send-email-suzuki.poulose@arm.com> <1444821634-1689-4-git-send-email-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1444821634-1689-4-git-send-email-suzuki.poulose@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 14, 2015 at 12:20:26PM +0100, Suzuki K. Poulose wrote: > Introduce helpers for finding the number of page table > levels required for a given VA width, shift for a particular > page table level. > > Convert the existing users to the new helpers. More users > to follow. > > Cc: Ard Biesheuvel > Cc: Mark Rutland > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Marc Zyngier > Signed-off-by: Suzuki K. Poulose > > --- > Changes since V2: > - Add comments around the macros > - Change ARM64_HW_PGTABLE_LEVEL_SHIFT to accept pagetable level as > described by ARM ARM > --- > arch/arm64/include/asm/pgtable-hwdef.h | 25 ++++++++++++++++++++++--- > 1 file changed, 22 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h > index 95c1ec0..c6194ab 100644 > --- a/arch/arm64/include/asm/pgtable-hwdef.h > +++ b/arch/arm64/include/asm/pgtable-hwdef.h > @@ -16,13 +16,31 @@ > #ifndef __ASM_PGTABLE_HWDEF_H > #define __ASM_PGTABLE_HWDEF_H > > +/* > + * Number of page-table levels required to address 'va_bits' wide > + * address, without section mapping. We resolve the top (va_bits - PAGE_SHIFT) > + * bits with (PAGE_SHIFT - 3) bits at each page table level. Hence: > + * > + * levels = DIV_ROUND_UP((va_bits - PAGE_SHIFT), (PAGE_SHIFT - 3)) > + * > + * We cannot include linux/kernel.h which defines DIV_ROUND_UP here > + * due to build issues. So we use the following magic formula. > + */ > +#define ARM64_HW_PGTABLE_LEVELS(va_bits) (((va_bits) - 4) / (PAGE_SHIFT - 3)) I think I failed the interview question [1]. :( I read the comment to mean this was a brand-new piece of magic, as opposed to a constant-folded copy of DIV_ROUND_UP. So it seems there's still some scope for confusion, even if that only includes me. I think we should bite the bullet and have a full copy of DIV_ROUND_UP, e.g. /* * We cannot include linux/kernel.h for DIV_ROUND_UP due to build * issues. Instead, copy & paste its magic formula here for now. */ #define __DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) /* * Number of page-table levels required to address 'va_bits' wide * address, without section mapping. We resolve the top (va_bits - PAGE_SHIFT) * bits with (PAGE_SHIFT - 3) bits at each page table level. */ #define ARM64_HW_PGTABLE_LEVELS(va_bits) \ __DIV_ROUND_UP((va_bits - PAGE_SHIFT), (PAGE_SHIFT - 3)) It's a little verbose, but it keeps this legible and ensures I get the job. We can leave the constant-folding to the compiler. Other than that, this looks good to me. With the above applied: Acked-by: Mark Rutland Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-October/375609.html