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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 1FE3AC4332D for ; Fri, 20 Mar 2020 13:04:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EECE42070A for ; Fri, 20 Mar 2020 13:04:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727176AbgCTNEu (ORCPT ); Fri, 20 Mar 2020 09:04:50 -0400 Received: from foss.arm.com ([217.140.110.172]:48652 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727015AbgCTNEt (ORCPT ); Fri, 20 Mar 2020 09:04:49 -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 E9AB21FB; Fri, 20 Mar 2020 06:04:48 -0700 (PDT) Received: from [10.37.12.155] (unknown [10.37.12.155]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B1B3F3F85E; Fri, 20 Mar 2020 06:04:44 -0700 (PDT) Subject: Re: [PATCH v4 18/26] arm64: vdso32: Replace TASK_SIZE_32 check in vgettimeofday To: Catalin Marinas Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, linux-mips@vger.kernel.org, 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: <20200317122220.30393-1-vincenzo.frascino@arm.com> <20200317122220.30393-19-vincenzo.frascino@arm.com> <20200317143834.GC632169@arrakis.emea.arm.com> <20200317155031.GD632169@arrakis.emea.arm.com> <83aaf9e1-0a8f-4908-577a-23766541b2ba@arm.com> <20200317174806.GE632169@arrakis.emea.arm.com> <93cfe94a-c2a3-1025-bc9c-e7c3fd891100@arm.com> <20200318183603.GF94111@arrakis.emea.arm.com> <1bc25a53-7a59-0f60-ecf2-a3cace46b823@arm.com> <20200319181004.GA29214@mbp> From: Vincenzo Frascino Message-ID: Date: Fri, 20 Mar 2020 13:05:14 +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: <20200319181004.GA29214@mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Catalin, On 3/19/20 6:10 PM, Catalin Marinas wrote: > Hi Vincenzo, > > On Thu, Mar 19, 2020 at 12:38:42PM +0000, Vincenzo Frascino wrote: >> On 3/18/20 6:36 PM, Catalin Marinas wrote: >>> On Wed, Mar 18, 2020 at 04:14:26PM +0000, Vincenzo Frascino wrote: >>>> On 3/17/20 5:48 PM, Catalin Marinas wrote: >>>>> So clock_gettime() on arm32 always falls back to the syscall? >>>> >>>> This seems not what you asked, and I think I answered accordingly. Anyway, in >>>> the case of arm32 the error code path is handled via syscall fallback. >>>> >>>> Look at the code below as an example (I am using getres because I know this >>>> email will be already too long, and I do not want to add pointless code, but the >>>> concept is the same for gettime and the others): >>>> >>>> static __maybe_unused >>>> int __cvdso_clock_getres(clockid_t clock, struct __kernel_timespec *res) >>>> { >>>> int ret = __cvdso_clock_getres_common(clock, res); >>>> >>>> if (unlikely(ret)) >>>> return clock_getres_fallback(clock, res); >>>> return 0; >>>> } >>>> >>>> When the return code of the "vdso" internal function returns an error the system >>>> call is triggered. >>> >>> But when __cvdso_clock_getres_common() does *not* return an error, it >>> means that it handled the clock_getres() call without a fallback to the >>> syscall. I assume this is possible on arm32. When the clock_getres() is >>> handled directly (not as a syscall), why doesn't arm32 need the same >>> (res >= TASK_SIZE) check? >> >> Ok, I see what you mean. > > I'm not sure. > Thank you for the long chat this morning. As we agreed I am going to repost the patches removing the checks discussed in this thread and we will address the syscall ABI difference subsequently with a different series. -- Regards, Vincenzo