From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752308AbeBHQbx (ORCPT ); Thu, 8 Feb 2018 11:31:53 -0500 Received: from foss.arm.com ([217.140.101.70]:37274 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986AbeBHQbv (ORCPT ); Thu, 8 Feb 2018 11:31:51 -0500 Subject: Re: [PATCH 1/2] arm64: capabilities: Allow flexibility in scope To: Dave Martin Cc: mark.rutland@arm.com, ckadabi@codeaurora.org, ard.biesheuvel@linaro.org, marc.zyngier@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, jnair@caviumnetworks.com, linux-arm-kernel@lists.infradead.org References: <86f23003-72bc-5bfc-af40-a92cc68def45@arm.com> <20180208121238.18792-1-suzuki.poulose@arm.com> <20180208161015.GZ5862@e103592.cambridge.arm.com> From: Suzuki K Poulose Message-ID: <08474a1a-3abd-9b89-ce75-d01e4b6fa659@arm.com> Date: Thu, 8 Feb 2018 16:31:47 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <20180208161015.GZ5862@e103592.cambridge.arm.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/18 16:10, Dave Martin wrote: > On Thu, Feb 08, 2018 at 12:12:37PM +0000, Suzuki K Poulose wrote: >> So far we have restricted the scopes for the capabilities >> as follows : >> 1) Errata workaround check are run all CPUs (i.e, always >> SCOPE_LOCAL_CPU) >> 2) Arm64 features are run only once after the sanitised >> feature registers are available using the SCOPE_SYSTEM. >> >> This prevents detecting cpu features that can be detected >> on one or more CPUs with SCOPE_LOCAL_CPU (e.g KPTI). Similarly >> for errata workaround with SCOPE_SYSTEM. >> >> This patch makes sure that we allow flexibility of having >> any scope for a capability. So, we now run through both >> arm64_features and arm64_errata in two phases for detection: >> >> a) with SCOPE_LOCAL_CPU filter on each boot time enabled >> CPUs. >> b) with SCOPE_SYSTEM filter only once after all boot time >> enabled CPUs are active. >> >> >> static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new) >> @@ -1387,13 +1389,15 @@ static void verify_local_cpu_errata_workarounds(void) >> static void update_cpu_errata_workarounds(void) >> { >> update_cpu_capabilities(arm64_errata, >> - ARM64_CPUCAP_SCOPE_ALL, >> + ARM64_CPUCAP_SCOPE_LOCAL_CPU, > > In isolation, this looks strange because it seems to handle only a > subset of arm64_errata now. > > I think I understand the change as follows: > > * all previously-existing errata workarounds SCOPE_LOCAL_CPU > anyway, so the behavior here doesn't change for any existing > caps; > > * the non SCOPE_SYSTEM workarounds (which this patch prepares for) "the SCOPE_SYSTEM" workarounds..." > are handled by the new setup_errata_workaround() path. > > Similarly, the features handling is split into two: one mirroring > the current behaviour (for SCOPE_SYSTEM this time) and one handling> the rest, for supporting SCOPE_CPU_LOCAL features in subsequent > patches. Right. The changes here are : New behavior: - Run SCOPE_LOCAL_CPU filter on arm64_features on all CPUs (newly added with this patch) via (newly added)update_cpu_local_features(). Split of existing behavior: - Run SCOPE_LOCAL_CPU(instead of the earlier SCOPE_ALL) on all CPUs in update_cpu_errata_workarounds() - Run SCOPE_SYSTEM filter on arm64_errata, once, via setup_errata_workarounds() > > Does that sound right? > > I'm not sure we need extra comments or documentation; I just want > to check that I've understood the patch correctly. So, would you prefer this split to the original patch ? Cheers Suzuki