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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EE2CCC433E0 for ; Tue, 12 Jan 2021 11:50:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BBD8223104 for ; Tue, 12 Jan 2021 11:50:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731262AbhALLu6 (ORCPT ); Tue, 12 Jan 2021 06:50:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:38008 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730146AbhALLu6 (ORCPT ); Tue, 12 Jan 2021 06:50:58 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 05C6F23104; Tue, 12 Jan 2021 11:50:17 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kzIBi-006wqv-RB; Tue, 12 Jan 2021 11:50:14 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Tue, 12 Jan 2021 11:50:14 +0000 From: Marc Zyngier To: Suzuki K Poulose Cc: Catalin Marinas , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Will Deacon , Mark Rutland , David Brazdil , Alexandru Elisei , Ard Biesheuvel , Jing Zhang , Ajay Patil , Prasad Sodagudi , Srinivas Ramana , James Morse , Julien Thierry , kernel-team@android.com Subject: Re: [PATCH v3 09/21] arm64: cpufeature: Add global feature override facility In-Reply-To: References: <20210111132811.2455113-1-maz@kernel.org> <20210111132811.2455113-10-maz@kernel.org> <20210111184154.GC17941@gaia> <129db8bd3913a90c96d4cfe4f55e27a0@kernel.org> User-Agent: Roundcube Webmail/1.4.9 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, mark.rutland@arm.com, dbrazdil@google.com, alexandru.elisei@arm.com, ardb@kernel.org, jingzhangos@google.com, pajay@qti.qualcomm.com, psodagud@codeaurora.org, sramana@codeaurora.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Suzuki, On 2021-01-12 09:17, Suzuki K Poulose wrote: > Hi Marc, > > On 1/11/21 7:48 PM, Marc Zyngier wrote: [...] >> diff --git a/arch/arm64/kernel/cpufeature.c >> b/arch/arm64/kernel/cpufeature.c >> index 894af60b9669..00d99e593b65 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -774,6 +774,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, >> u64 new) >>      u64 strict_mask = ~0x0ULL; >>      u64 user_mask = 0; >>      u64 valid_mask = 0; >> +    u64 override_val = 0, override_mask = 0; >> >>      const struct arm64_ftr_bits *ftrp; >>      struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg); >> @@ -781,9 +782,35 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, >> u64 new) >>      if (!reg) >>          return; >> >> +    if (reg->override_mask && reg->override_val) { >> +        override_mask = *reg->override_mask; >> +        override_val = *reg->override_val; >> +    } >> + >>      for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) { >>          u64 ftr_mask = arm64_ftr_mask(ftrp); >>          s64 ftr_new = arm64_ftr_value(ftrp, new); >> +        s64 ftr_ovr = arm64_ftr_value(ftrp, override_val); >> + >> +        if ((ftr_mask & override_mask) == ftr_mask) { >> +            if (ftr_ovr < ftr_new) { > > Here we assume that all the features are FTR_LOWER_SAFE. We could > probably use arm64_ftr_safe_value(ftrp, ftr_new, ftr_ovr) here ? > That would cover us for both HIGHER_SAFE and LOWER_SAFE features. > However that may be restrictive for FTR_EXACT, as we the safe > value would be set to "ftr->safe_val". I guess that may be better > than forcing to use an unsafe value for the boot CPU, which could > anyway conflict with the other CPUs and eventually trigger the > ftr alue to be safe_val. I like the idea of using the helper, as it cleanups up the code a bit. However, not being to set a feature to a certain value could be restrictive, as in general, it means that we can only disable a feature and not adjust its level of support. Take PMUVER for example: with the helper, I can't override it from v8.4 to v8.1. I can only go to v8.0. Is it something we care about? Thanks, M. -- Jazz is not dead. It just smells funny...