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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 80791C433B4 for ; Thu, 8 Apr 2021 21:49:31 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D7F90610E6 for ; Thu, 8 Apr 2021 21:49:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D7F90610E6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Cc:To:Subject:Message-ID:Date:From:In-Reply-To: References:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9CiilZm1YEULMENudUcP8b2XQnw8AZ0HUYTQCdAW72g=; b=QAk7urx/HEDNIwONPlV/KIMih In57K/bgOYvvyPCEjx6qggtXnZ7cjN6B0QFGajVZrT9saFw64Ds0QXlhu9eoYrya6XKh+Eh2iVgrz 7hf0DCp0xXavhocTOfL+vszhuJEgIE33fnOWTwnXQKU1MfD6QOs/FQQBzVsjlVXFCWGdpXRMc0qE0 DTlJIxSBn4F6MSR15xsocs2eEuE6ukjzNlqv9re7d4uXLK9P6xk7kBjNWltRqC5MWRQEumE351SB3 JqozlC9fSFbUcmrbygioVaza7s77AHpmFspT0ZOK/V8tKo4NF/g9JQKUaXduZzjIbjDf04LeS6lzu +qGcGFVuQ==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lUcVR-009KMa-Rh; Thu, 08 Apr 2021 21:48:06 +0000 Received: from mail.kernel.org ([198.145.29.99]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lUcVM-009KKz-Bd for linux-arm-kernel@lists.infradead.org; Thu, 08 Apr 2021 21:48:02 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7FDE6610E6 for ; Thu, 8 Apr 2021 21:47:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1617918475; bh=LQYc0IlC9BHgstHzJ0btuYChD0Q1jwP6n5ycmhTo3Dw=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=rKjVXeE9flsUCU90Z4tBmiIS3LRoUt5xXp5r9LDIWO7vK19c70YiUvRD6XNyKLQ6y Bu3SEj8kaeruXr+bswayVNMGhGUeyJPhsDea7Q+boO7oMPm1nRUpsDuii6hEJvQIp6 +XbzoRMpXGogVEvh3y//1kkIVsw42oGOe1zQ/UxFB6MelavcL5PzMl+EBmK7IBh047 EFRqGu2Jj2nSu1vUb6notXDhnHPg3/XgiIdfSpaWFyAuu4CoeXEqQprmWAM5/Et4gz EajsscmhgDPvXY6WXcbpDQAIEsCGi8eBx4KNL4wqpFis9Gjj9kR5wLf47ogwrTasia cum5H4wMX/fVg== Received: by mail-oo1-f43.google.com with SMTP id j10-20020a4ad18a0000b02901b677a0ba98so870221oor.1 for ; Thu, 08 Apr 2021 14:47:55 -0700 (PDT) X-Gm-Message-State: AOAM532UjcN0zyxP03Ne5+pvzR5hDM7snJYT3yNTS2/3Ywr8AQJMdhIj xAnLmL9eX7ueZlSXBaiyPLJgRBL1k0Rp+u9r/vE= X-Google-Smtp-Source: ABdhPJy7qgMXVKW8m7GVpJrqBw3Z0vJ596jqjCNZDnqqDSWcC51Pn+VHPI7eCmp6LEQ4gMI/cNgWDbrC+1DKyNQ1hm8= X-Received: by 2002:a4a:304a:: with SMTP id z10mr9423708ooz.26.1617918474746; Thu, 08 Apr 2021 14:47:54 -0700 (PDT) MIME-Version: 1.0 References: <20210408131010.1109027-1-maz@kernel.org> <20210408131010.1109027-4-maz@kernel.org> In-Reply-To: <20210408131010.1109027-4-maz@kernel.org> From: Arnd Bergmann Date: Thu, 8 Apr 2021 23:47:38 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/3] arm64: Get rid of CONFIG_ARM64_VHE To: Marc Zyngier Cc: Linux ARM , Hector Martin , Mark Rutland , Will Deacon , Catalin Marinas , Android Kernel Team X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210408_224800_618733_5EBB2548 X-CRM114-Status: GOOD ( 18.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Apr 8, 2021 at 3:10 PM Marc Zyngier wrote: > > CONFIG_ARM64_VHE was introduced with ARMv8.1 (some 7 years ago), > and has been enabled by default for almost all that time. > > Given that newer systems that are VHE capable are finally becoming > available, and that some systems are even incapable of not running VHE, > drop the configuration altogether. > > Anyone willing to stick to non-VHE on VHE hardware for obscure > reasons should use the 'kvm-arm.mode=nvhe' command-line option. Have you considered adding options to do the reverse logic for this and other features, such as making support for the old non-VHE optional at compile time? I understand that so far the rule is (almost) always that an arm64 kernel should run on any Armv8.0-A or higher system regardless of configuration, but the now announced Armv9.0-A definition might be the chance to introduce the concept of a minimum level the way we do on other architectures (e.g. armv6/v6k/v7 or k8/pentium4/core2/atom/generic). The way I can see this working would be to have a single user-visible option that controls whether the kernel supports only Armv9.0-A/Armv8.5-A and assumes all mandatory features of that are present, or it remains as before and supports all implementations back to the first v8. This would help eliminate the runtime detection for not just VHE but also LSE, LPA, PAN, etc. Not sure how significant the cost of any of those are in terms of runtime performance and/or code size, but it would feel nice to be able to build a kernel that can actually rely on sane hardware features even if it will take a few more years before that hardware becomes common enough to actually get some distros ship a kernel that requires v8.5/v9.0. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel