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 F34E8C433F5 for ; Thu, 30 Sep 2021 10:29:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C42126197A for ; Thu, 30 Sep 2021 10:29:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349923AbhI3Kbf (ORCPT ); Thu, 30 Sep 2021 06:31:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:40692 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349904AbhI3Kbe (ORCPT ); Thu, 30 Sep 2021 06:31:34 -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 0DD6F61882; Thu, 30 Sep 2021 10:29:52 +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 1mVtK2-00DxJW-4B; Thu, 30 Sep 2021 11:29:50 +0100 Date: Thu, 30 Sep 2021 11:29:49 +0100 Message-ID: <87a6jutkyq.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: <5bc623f2-e4c1-cc9c-683c-2f95648f1a68@arm.com> References: <20210903091652.985836-1-maz@kernel.org> <5bc623f2-e4c1-cc9c-683c-2f95648f1a68@arm.com> 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 Wed, 29 Sep 2021 11:35:46 +0100, Suzuki K Poulose wrote: > > On 03/09/2021 10:16, Marc Zyngier wrote: > > Although KVM can be compiled out of the kernel, it cannot be disabled > > at runtime. Allow this possibility by introducing a new mode that > > will prevent KVM from initialising. > > > > This is useful in the (limited) circumstances where you don't want > > KVM to be available (what is wrong with you?), or when you want > > to install another hypervisor instead (good luck with that). > > > > Signed-off-by: Marc Zyngier > > --- > > Documentation/admin-guide/kernel-parameters.txt | 3 +++ > > arch/arm64/include/asm/kvm_host.h | 1 + > > arch/arm64/kernel/idreg-override.c | 1 + > > arch/arm64/kvm/arm.c | 14 +++++++++++++- > > 4 files changed, 18 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index 91ba391f9b32..cc5f68846434 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -2365,6 +2365,9 @@ > > kvm-arm.mode= > > [KVM,ARM] Select one of KVM/arm64's modes of operation. > > + none: Forcefully disable KVM and run in nVHE > > mode, > > + preventing KVM from ever initialising. > > + > > nvhe: Standard nVHE-based mode, without support for > > protected guests. > > diff --git a/arch/arm64/include/asm/kvm_host.h > > b/arch/arm64/include/asm/kvm_host.h > > index f8be56d5342b..019490c67976 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -58,6 +58,7 @@ > > enum kvm_mode { > > KVM_MODE_DEFAULT, > > KVM_MODE_PROTECTED, > > + KVM_MODE_NONE, > > }; > > enum kvm_mode kvm_get_mode(void); > > diff --git a/arch/arm64/kernel/idreg-override.c > > b/arch/arm64/kernel/idreg-override.c > > index d8e606fe3c21..57013c1b6552 100644 > > --- a/arch/arm64/kernel/idreg-override.c > > +++ b/arch/arm64/kernel/idreg-override.c > > @@ -95,6 +95,7 @@ static const struct { > > char alias[FTR_ALIAS_NAME_LEN]; > > char feature[FTR_ALIAS_OPTION_LEN]; > > } aliases[] __initconst = { > > + { "kvm-arm.mode=none", "id_aa64mmfr1.vh=0" }, > > { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" }, > > { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" }, > > { "arm64.nobti", "id_aa64pfr1.bt=0" }, > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index fe102cd2e518..cdc70e238316 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque) > > return -ENODEV; > > } > > + if (kvm_get_mode() == KVM_MODE_NONE) { > > + kvm_info("KVM disabled from command line\n"); > > + return -ENODEV; > > + } > > + > > in_hyp_mode = is_kernel_in_hyp_mode(); > > if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) > > || > > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg) > > return 0; > > } > > - if (strcmp(arg, "nvhe") == 0 && > > !WARN_ON(is_kernel_in_hyp_mode())) > > + if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) { > > + kvm_mode = KVM_MODE_DEFAULT; > > return 0; > > + } > > + > > + 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). We could add another option (none-vhe?) that stays at EL2 and still disables KVM if there is an appetite for it. > Otherwise, > > Acked-by: Suzuki K Poulose > Thanks, M. -- Without deviation from the norm, progress is not possible.