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=-9.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 27582C43461 for ; Tue, 8 Sep 2020 05:13:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E301A2166E for ; Tue, 8 Sep 2020 05:13:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728556AbgIHFNy (ORCPT ); Tue, 8 Sep 2020 01:13:54 -0400 Received: from foss.arm.com ([217.140.110.172]:48166 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725938AbgIHFNy (ORCPT ); Tue, 8 Sep 2020 01:13:54 -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 C727731B; Mon, 7 Sep 2020 22:13:53 -0700 (PDT) Received: from [10.163.71.211] (unknown [10.163.71.211]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BE6303F73C; Mon, 7 Sep 2020 22:13:49 -0700 (PDT) Subject: Re: [PATCH V3] arm64/cpuinfo: Define HWCAP name arrays per their actual bit definitions To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, Mark Brown , Dave Martin , Ard Biesheuvel , Mark Rutland , Suzuki K Poulose , linux-kernel@vger.kernel.org References: <1597665863-564-1-git-send-email-anshuman.khandual@arm.com> <20200907121611.GA12237@willie-the-truck> From: Anshuman Khandual Message-ID: Date: Tue, 8 Sep 2020 10:43:12 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200907121611.GA12237@willie-the-truck> 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 On 09/07/2020 05:46 PM, Will Deacon wrote: > On Mon, Aug 17, 2020 at 05:34:23PM +0530, Anshuman Khandual wrote: >> HWCAP name arrays (hwcap_str, compat_hwcap_str, compat_hwcap2_str) that are >> scanned for /proc/cpuinfo are detached from their bit definitions making it >> vulnerable and difficult to correlate. It is also bit problematic because >> during /proc/cpuinfo dump these arrays get traversed sequentially assuming >> they reflect and match actual HWCAP bit sequence, to test various features >> for a given CPU. This redefines name arrays per their HWCAP bit definitions >> . It also warns after detecting any feature which is not expected on arm64. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Mark Brown >> Cc: Dave Martin >> Cc: Ard Biesheuvel >> Cc: Mark Rutland >> Cc: Suzuki K Poulose >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual >> --- >> This applies on 5.9-rc1 >> >> Mark, since the patch has changed I have dropped your Acked-by: tag. Are you >> happy to give a new one ? >> >> Changes in V3: >> >> - Moved name arrays to (arch/arm64/kernel/cpuinfo.c) to prevent a build warning >> - Replaced string values with NULL for all compat features not possible on arm64 >> - Changed compat_hwcap_str[] iteration on size as some NULL values are expected >> - Warn once after detecting any feature on arm64 that is not expected >> >> Changes in V2: (https://patchwork.kernel.org/patch/11533755/) >> >> - Defined COMPAT_KERNEL_HWCAP[2] and updated the name arrays per Mark >> - Updated the commit message as required >> >> Changes in V1: (https://patchwork.kernel.org/patch/11532945/) >> >> arch/arm64/include/asm/hwcap.h | 9 +++ >> arch/arm64/kernel/cpuinfo.c | 172 ++++++++++++++++++++++------------------- >> 2 files changed, 100 insertions(+), 81 deletions(-) > > [...] > >> + [KERNEL_HWCAP_FP] = "fp", >> + [KERNEL_HWCAP_ASIMD] = "asimd", >> + [KERNEL_HWCAP_EVTSTRM] = "evtstrm", >> + [KERNEL_HWCAP_AES] = "aes", > > It would be nice if the cap and the string were generated by the same > macro, along the lines of: > > #define KERNEL_HWCAP(c) [KERNEL_HWCAP_##c] = #c, > > Does making the constants mixed case break anything, or is it just really > churny to do? Currently all existing HWCAP feature strings are lower case, above change will make them into upper case instead. I could not find a method to force convert #c into lower case constant strings in the macro definition. Would not changing the HWCAP string case here, break user interface ? > >> @@ -166,9 +167,18 @@ static int c_show(struct seq_file *m, void *v) >> seq_puts(m, "Features\t:"); >> if (compat) { >> #ifdef CONFIG_COMPAT >> - for (j = 0; compat_hwcap_str[j]; j++) >> - if (compat_elf_hwcap & (1 << j)) >> + for (j = 0; j < ARRAY_SIZE(compat_hwcap_str); j++) { >> + if (compat_elf_hwcap & (1 << j)) { >> + /* >> + * Warn once if any feature should not >> + * have been present on arm64 platform. >> + */ >> + if (WARN_ON_ONCE(!compat_hwcap_str[j])) >> + continue; >> + >> seq_printf(m, " %s", compat_hwcap_str[j]); >> + } >> + } >> >> for (j = 0; compat_hwcap2_str[j]; j++) > > Hmm, I find this pretty confusing now as compat_hwcap_str is not NULL > terminated and must be traversed with a loop bounded by ARRAY_SIZE(...), Right. Thats because unlike before, it can now have some intermediate NULL entries. Hence NULL sentinel based traversal wont be possible any more. > whereas compat_hwcap2_str *is* NULL terminated and is traversed until you > hit the sentinel. > > I think hwcap_str, compat_hwcap_str and compat_hwcap2_str should be > identical in this regard. Sure, will make the traversal based on ARRAY_SIZE() for all three arrays here, to make that uniform. > > Will >