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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 B8F1BC18E5B for ; Mon, 16 Mar 2020 10:54:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99E5820719 for ; Mon, 16 Mar 2020 10:54:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730582AbgCPKyj (ORCPT ); Mon, 16 Mar 2020 06:54:39 -0400 Received: from foss.arm.com ([217.140.110.172]:46096 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730529AbgCPKyj (ORCPT ); Mon, 16 Mar 2020 06:54:39 -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 5497431B; Mon, 16 Mar 2020 03:54:38 -0700 (PDT) Received: from [10.37.9.38] (unknown [10.37.9.38]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 240FD3F52E; Mon, 16 Mar 2020 03:54:32 -0700 (PDT) Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h To: Catalin Marinas Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, clang-built-linux@googlegroups.com, x86@kernel.org, Will Deacon , Arnd Bergmann , Russell King , Paul Burton , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Stephen Boyd , Mark Salyzyn , Kees Cook , Peter Collingbourne , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nick Desaulniers , Marc Zyngier , Mark Rutland , Will Deacon References: <20200313154345.56760-1-vincenzo.frascino@arm.com> <20200313154345.56760-19-vincenzo.frascino@arm.com> <20200315182950.GB32205@mbp> <20200316103437.GD3005@mbp> From: Vincenzo Frascino Message-ID: <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> Date: Mon, 16 Mar 2020 10:55:00 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200316103437.GD3005@mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi Catalin, On 3/16/20 10:34 AM, Catalin Marinas wrote: [...] >> >> I tried to fine grain the headers as much as I could in order to avoid >> unneeded/unwanted inclusions: >> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to >> arch/arm64/kernel/vdso32/vgettimeofday.c). > > I see. But the test is probably useless. With 4K pages, TASK_SIZE_32 is > 1UL << 32, so you can't have a u32 greater than this. So I'd argue that > the ABI compatibility here doesn't matter. > > With 16K or 64K pages, TASK_SIZE_32 is slightly smaller but arm32 never > supported it. > > What's the side-effect of dropping this check altogether? > The main side-effect is that arm32 and arm64 compat have a different behavior, that it is what we want to avoid. The vdsotest [1] I am using, verifies all the side conditions with respect to the ABI, which we are now compatible with. Removing those checks would break this condition. [1] https://github.com/nlynch-mentor/vdsotest -- Regards, Vincenzo