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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 774D1C433F5 for ; Fri, 1 Oct 2021 14:54:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5261A61A0A for ; Fri, 1 Oct 2021 14:54:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354667AbhJAOz5 (ORCPT ); Fri, 1 Oct 2021 10:55:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:39860 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231764AbhJAOzy (ORCPT ); Fri, 1 Oct 2021 10:55:54 -0400 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 C22B5619E7; Fri, 1 Oct 2021 14:54:10 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mWJvM-00EDTt-R2; Fri, 01 Oct 2021 15:54:08 +0100 Date: Fri, 01 Oct 2021 15:54:08 +0100 Message-ID: <87ee94ssmn.wl-maz@kernel.org> From: Marc Zyngier To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, ascull@google.com, dbrazdil@google.com, James Morse , Alexandru Elisei , kernel-team@android.com Subject: Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line In-Reply-To: References: <20210903091652.985836-1-maz@kernel.org> <5bc623f2-e4c1-cc9c-683c-2f95648f1a68@arm.com> <87a6jutkyq.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, ascull@google.com, dbrazdil@google.com, james.morse@arm.com, alexandru.elisei@arm.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: kvm@vger.kernel.org On Fri, 01 Oct 2021 10:27:18 +0100, Suzuki K Poulose wrote: > > On 30/09/2021 11:29, Marc Zyngier wrote: > > On Wed, 29 Sep 2021 11:35:46 +0100, > > Suzuki K Poulose wrote: > >> > >>> + if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) { > >> > >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the > >> user wants to keep the KVM out of the picture for, say debugging > >> something, it is perfectly Ok to allow the kernel to be running at EL2 > >> without having to change the Firmware to alter the landing EL for the > >> kernel ? > > > > Well, the doc says "run in nVHE mode" and the option forces > > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW > > that is VHE only. Note that this doesn't rely on any firmware change > > (we drop from EL2 to EL1 and stay there). > > Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I > missed. TBH, that name to me sounds like "no KVM" at all, which is what > we want. The question is, do we really need "none" to force vh == 0 ? I > understand this is only a problem on a rare set of HWs. But the generic > option looks deceiving. > > That said, I am happy to leave this as is and the doc says so. I think you have a point here. Conflating the two things is a bit odd, and we might as well let the user pick the configuration they want (they can always pass 'id_aa64mmfr1.vh=0' themselves). I'll respin the patch with this change. Thanks, M. -- Without deviation from the norm, progress is not possible.