From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1A6EC433E6 for ; Mon, 13 Jul 2020 12:21:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A44B420738 for ; Mon, 13 Jul 2020 12:21:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729761AbgGMMV5 (ORCPT ); Mon, 13 Jul 2020 08:21:57 -0400 Received: from foss.arm.com ([217.140.110.172]:59286 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726586AbgGMMV4 (ORCPT ); Mon, 13 Jul 2020 08:21:56 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3E83530E; Mon, 13 Jul 2020 05:21:56 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AA0163F887; Mon, 13 Jul 2020 05:21:54 -0700 (PDT) Date: Mon, 13 Jul 2020 13:21:48 +0100 From: Mark Rutland To: Christoph Hellwig , Geert Uytterhoeven Cc: Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Andrew Morton , Linus Torvalds , linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/6] uaccess: add force_uaccess_{begin,end} helpers Message-ID: <20200713122148.GA51007@lakrids.cambridge.arm.com> References: <20200710135706.537715-1-hch@lst.de> <20200710135706.537715-6-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200710135706.537715-6-hch@lst.de> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 10, 2020 at 03:57:05PM +0200, Christoph Hellwig wrote: > Add helpers to wraper the get_fs/set_fs magic for undoing any damange > done by set_fs(KERNEL_DS). There is no real functional benefit, but this > documents the intent of these calls better, and will allow stubbing the > functions out easily for kernels builds that do not allow address space > overrides in the future. > diff --git a/arch/m68k/include/asm/tlbflush.h b/arch/m68k/include/asm/tlbflush.h > index 191e75a6bb249e..30471549e1e224 100644 > --- a/arch/m68k/include/asm/tlbflush.h > +++ b/arch/m68k/include/asm/tlbflush.h > @@ -13,13 +13,13 @@ static inline void flush_tlb_kernel_page(void *addr) > if (CPU_IS_COLDFIRE) { > mmu_write(MMUOR, MMUOR_CNL); > } else if (CPU_IS_040_OR_060) { > - mm_segment_t old_fs = get_fs(); > - set_fs(KERNEL_DS); > + mm_segment_t old_fs = force_uaccess_begin(); > + This used to set KERNEL_DS, and now it sets USER_DS, which looks wrong superficially. If the new behaviour is fine it suggests that the old behaviour was wrong, or that this is superfluous and could go entirely. Geert? Mark. > __asm__ __volatile__(".chip 68040\n\t" > "pflush (%0)\n\t" > ".chip 68k" > : : "a" (addr)); > - set_fs(old_fs); > + force_uaccess_end(old_fs); > } else if (CPU_IS_020_OR_030) > __asm__ __volatile__("pflush #4,#4,(%0)" : : "a" (addr)); > +/* > + * Force the uaccess routines to be wired up for actual userspace access, > + * overriding any possible set_fs(KERNEL_DS) still lingering around. Undone > + * using force_uaccess_end below. > + */ > +static inline mm_segment_t force_uaccess_begin(void) > +{ > + mm_segment_t fs = get_fs(); > + > + set_fs(USER_DS); > + return fs; > +} > + > +static inline void force_uaccess_end(mm_segment_t oldfs) > +{ > + set_fs(oldfs); > +}