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 10168C43603 for ; Thu, 12 Dec 2019 15:22:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D57F0206A5 for ; Thu, 12 Dec 2019 15:22:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729139AbfLLPWQ (ORCPT ); Thu, 12 Dec 2019 10:22:16 -0500 Received: from foss.arm.com ([217.140.110.172]:50530 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728929AbfLLPWQ (ORCPT ); Thu, 12 Dec 2019 10:22:16 -0500 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 A559030E; Thu, 12 Dec 2019 07:22:15 -0800 (PST) Received: from [10.1.197.1] (ewhatever.cambridge.arm.com [10.1.197.1]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 88AC73F6CF; Thu, 12 Dec 2019 07:22:14 -0800 (PST) Subject: Re: [PATCH] arm64: Introduce ISAR6 CPU ID register To: Mark Rutland , Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Marc Zyngier , James Morse , linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu References: <1576145663-9909-1-git-send-email-anshuman.khandual@arm.com> <20191212144633.GE46910@lakrids.cambridge.arm.com> From: Suzuki Kuruppassery Poulose Message-ID: Date: Thu, 12 Dec 2019 15:22:13 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191212144633.GE46910@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed 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 12/12/2019 14:46, Mark Rutland wrote: > On Thu, Dec 12, 2019 at 03:44:23PM +0530, Anshuman Khandual wrote: >> +#define ID_ISAR6_JSCVT_SHIFT 0 >> +#define ID_ISAR6_DP_SHIFT 4 >> +#define ID_ISAR6_FHM_SHIFT 8 >> +#define ID_ISAR6_SB_SHIFT 12 >> +#define ID_ISAR6_SPECRES_SHIFT 16 >> +#define ID_ISAR6_BF16_SHIFT 20 >> +#define ID_ISAR6_I8MM_SHIFT 24 > >> @@ -399,6 +399,7 @@ static const struct __ftr_reg_entry { >> ARM64_FTR_REG(SYS_ID_ISAR4_EL1, ftr_generic_32bits), >> ARM64_FTR_REG(SYS_ID_ISAR5_EL1, ftr_id_isar5), >> ARM64_FTR_REG(SYS_ID_MMFR4_EL1, ftr_id_mmfr4), > >> + ARM64_FTR_REG(SYS_ID_ISAR6_EL1, ftr_generic_32bits), > > Using ftr_generic_32bits exposes the lowest-common-denominator for all > 4-bit fields in the register, and I don't think that's the right thing > to do here, because: > > * We have no idea what ID_ISAR6 bits [31:28] may mean in future. > > * AFAICT, the instructions described by ID_ISAR6.SPECRES (from the > ARMv8.0-PredInv extension) operate on the local PE and are not > broadcast. To make those work as a guest expects, the host will need > to do additional things (e.g. to preserve that illusion when a vCPU is > migrated from one pCPU to another and back). > > Given that, think we should add an explicit ftr_id_isar6 which only > exposes the fields that we're certain are safe to expose to a guest > (i.e. without SPECRES). Agree. Thanks for pointing this out. I recommended the usage of generic_32bits table without actually looking at the feature definitions. Anshuman, Sorry about this. Cheers Suzuki