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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E41B2C433F5 for ; Sun, 21 Nov 2021 12:37:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238253AbhKUMk3 (ORCPT ); Sun, 21 Nov 2021 07:40:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:44232 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238251AbhKUMk2 (ORCPT ); Sun, 21 Nov 2021 07:40:28 -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 8429260555; Sun, 21 Nov 2021 12:37:23 +0000 (UTC) Received: from ip-185-104-136-29.ptr.icomera.net ([185.104.136.29] helo=wait-a-minute.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 1mom5x-006sR9-Fi; Sun, 21 Nov 2021 12:37:21 +0000 Date: Sun, 21 Nov 2021 12:37:21 +0000 Message-ID: <87ilwlsn0e.wl-maz@kernel.org> From: Marc Zyngier To: Reiji Watanabe Cc: Eric Auger , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Will Deacon , Peter Shier , Paolo Bonzini , linux-arm-kernel@lists.infradead.org Subject: Re: [RFC PATCH v3 03/29] KVM: arm64: Introduce struct id_reg_info In-Reply-To: References: <20211117064359.2362060-1-reijiw@google.com> <20211117064359.2362060-4-reijiw@google.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: 185.104.136.29 X-SA-Exim-Rcpt-To: reijiw@google.com, eauger@redhat.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, will@kernel.org, pshier@google.com, pbonzini@redhat.com, linux-arm-kernel@lists.infradead.org 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, 19 Nov 2021 04:47:53 +0000, Reiji Watanabe wrote: > > I am going to add the following comment. Does it look clear enough for you ? > > /* > * This is an optional ID register specific validation function. > * When userspace tries to set the ID register, arm64_check_features() > * will check if the requested value indicates any features that cannot > * be supported by KVM on the host. But, some ID register fields need > * a special checking and this function can be used for such fields. > * e.g. KVM_CREATE_DEVICE must be used to configure GICv3 for a guest. > * ID_AA64PFR0_EL1.GIC shouldn't be set to 1 unless GICv3 is configured. There is no such requirement. GICv3 has a compatibility interface, and although KVM doesn't make use of it, there is no reason not to expose that GICv3 exists on the CPU even if not using it. Even more, this has been the case forever, and making this change now would probably break migration. M. -- Without deviation from the norm, progress is not possible.