From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751468AbdGMKTh (ORCPT ); Thu, 13 Jul 2017 06:19:37 -0400 Received: from foss.arm.com ([217.140.101.70]:36592 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751193AbdGMKTg (ORCPT ); Thu, 13 Jul 2017 06:19:36 -0400 Message-ID: <596748FB.20902@arm.com> Date: Thu, 13 Jul 2017 11:18:35 +0100 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Mark Rutland CC: ard.biesheuvel@linaro.org, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, akashi.takahiro@linaro.org, catalin.marinas@arm.com, dave.martin@arm.com, labbott@fedoraproject.org, will.deacon@arm.com, keescook@chromium.org Subject: Re: [RFC PATCH 2/6] arm64: avoid open-coding THREAD_SIZE{,_ORDER} References: <1499898783-25732-1-git-send-email-mark.rutland@arm.com> <1499898783-25732-3-git-send-email-mark.rutland@arm.com> In-Reply-To: <1499898783-25732-3-git-send-email-mark.rutland@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mark, On 12/07/17 23:32, Mark Rutland wrote: > Currently we define THREAD_SIZE_ORDER dependent on which arm64-specific > page size kconfig symbol was selected. This is unfortunate, as it hides > the relationship between THREAD_SIZE_ORDER and THREAD_SIZE, and makes it > painful more painful than necessary to modify the thread size as we will > need to do for some debug configurations. > > This patch follows arch/metag's approach of consistently defining > THREAD_SIZE in terms of THREAD_SIZE_ORDER. This avoids having ifdefs for > particular page size configurations, and allows us to change a single > definition to change the thread size. I think this has unintended side effects for 64K page systems. (or at least not yet intended) Today: > #ifdef CONFIG_ARM64_4K_PAGES > #define THREAD_SIZE_ORDER 2 > #elif defined(CONFIG_ARM64_16K_PAGES) > #define THREAD_SIZE_ORDER 0 > #endif Means THREAD_SIZE_ORDER is unset on 64K, and THREAD_SIZE is always: > #define THREAD_SIZE 16384 /kernel/fork.c matches this with its: > # if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) [...] > #else [...] > void thread_stack_cache_init(void) > { > thread_stack_cache = kmem_cache_create("thread_stack", THREAD_SIZE, > THREAD_SIZE, 0, NULL); > BUG_ON(thread_stack_cache == NULL); > } > #endif To create a kmemcache to share 64K pages as 16K stacks. After this patch: > #define THREAD_SHIFT 14 > > #if THREAD_SHIFT >= PAGE_SHIFT > #define THREAD_SIZE_ORDER (THREAD_SHIFT - PAGE_SHIFT) > #else > #define THREAD_SIZE_ORDER 0 > #endif Means THREAD_SIZE_ORDER is 0, and: > #define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER) gives us a 64K THREAD_SIZE. Thanks, James > diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h > index 141f13e9..6d0c59a 100644 > --- a/arch/arm64/include/asm/thread_info.h > +++ b/arch/arm64/include/asm/thread_info.h > @@ -23,13 +23,17 @@ > > #include > > -#ifdef CONFIG_ARM64_4K_PAGES > -#define THREAD_SIZE_ORDER 2 > -#elif defined(CONFIG_ARM64_16K_PAGES) > +#include > + > +#define THREAD_SHIFT 14 > + > +#if THREAD_SHIFT >= PAGE_SHIFT > +#define THREAD_SIZE_ORDER (THREAD_SHIFT - PAGE_SHIFT) > +#else > #define THREAD_SIZE_ORDER 0 > #endif > > -#define THREAD_SIZE 16384 > +#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER) > #define THREAD_START_SP (THREAD_SIZE - 16) > > #ifndef __ASSEMBLY__ >