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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1EF26C61DA4 for ; Thu, 9 Mar 2023 16:26:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Subject:Cc:To:From:Message-ID:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=GDqJfyuOvxNVRoQA8t4+oDTrsarOzq+V1O72JMD1wKM=; b=vGol2ECsGIDzyO 6XkwlPH+IVGqn3qTshsx4VPo6F5EhwmYqVdPbw3ac4BR8QO5REAd8YgZ6so4t0yO2bm0Em0Y2iQNN M88LTYTZ4OdOTHVzVf06A5Aq34LSpdj9OSm142MtSivhv/gBwD42pNCF1w7J+GMopO0Vw10XWswy3 NbH2gn7cX3oiIjsr0/AYfdCqg9y3lc8bILtSyi1KTtaQhohsnd2klstWL8COds4Ai8JJsDjZc09rX CzSbc/mod86qNXtRnTme2ttdwxuQ1zbp2DQ66d6CkYY3c43xSG6tuudhfkUgw4MVPKO6OiFJcgUuU /vCpuK4F5gfZsFVucoQQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1paJ4l-00BFgZ-DO; Thu, 09 Mar 2023 16:25:07 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1paJ4g-00BFfE-LI for linux-arm-kernel@lists.infradead.org; Thu, 09 Mar 2023 16:25:04 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7029861AD7; Thu, 9 Mar 2023 16:24:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA08BC433EF; Thu, 9 Mar 2023 16:24:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1678379098; bh=gDGW2AOKYosidRKLxmcTG6EkP1INMgYUF2kBjTMbU+I=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=f3tIyFuVZcxsYpepBEx1tK+D1V+rYK/um08l3A5YUcIYcdC7g4o8cZdexPGB/wJra Ws4NLmkXtObdxLukkV6iZzIwo1anVhDluI0ztKFdT5DZUUb3OFhyHO9Vr4D9BjChlp RMv8EVdUG2aIihRBWd1P7FIXP79OekFgEN4Off+cXO7cVEFtYgd0b7YZ0P88Z85mrC oQIcD2D7XdB5J1mv57NAF5VeEzOm1uWlwr9CnfaRNhEAbPVwI8QqmvE8mBRf0iqwbX EBAcJXSxegKoLGVlwqvBTn7+5fotATic2P6uJ83DsOpiyYxtkOCehVfTVeZYmSNy7i zGQJU0f1aTyVg== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1paJ4a-00GN2b-J6; Thu, 09 Mar 2023 16:24:56 +0000 Date: Thu, 09 Mar 2023 16:24:56 +0000 Message-ID: <86y1o5yjs7.wl-maz@kernel.org> From: Marc Zyngier To: Mark Brown Cc: Joey Gouly , linux-arm-kernel@lists.infradead.org, nd@arm.com, catalin.marinas@arm.com, james.morse@arm.com, mark.rutland@arm.com, oliver.upton@linux.dev, suzuki.poulose@arm.com, will@kernel.org, yuzenghui@huawei.com Subject: Re: [PATCH v1 11/18] KVM: arm64: expose ID_AA64MMFR3_EL1 to guests In-Reply-To: References: <20230309145246.22787-1-joey.gouly@arm.com> <20230309145246.22787-12-joey.gouly@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/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: broonie@kernel.org, joey.gouly@arm.com, linux-arm-kernel@lists.infradead.org, nd@arm.com, catalin.marinas@arm.com, james.morse@arm.com, mark.rutland@arm.com, oliver.upton@linux.dev, suzuki.poulose@arm.com, will@kernel.org, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230309_082502_775312_2208A824 X-CRM114-Status: GOOD ( 17.03 ) 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, 09 Mar 2023 16:07:42 +0000, Mark Brown wrote: > > [1 ] > On Thu, Mar 09, 2023 at 02:52:39PM +0000, Joey Gouly wrote: > > > Now that KVM context switches the appropriate registers, expose > > ID_AA64MMFR3_EL1 to guests to allow them to use the new features. > > Should we be adding new vCPU features given that there's new > architectural state here? What do we gain by that? AFAICT, it only makes the UAPI more complex. And to be honest, *any* new feature added to KVM results in new architectural state. Are we going to add more and more of these ad nauseam? It doesn't scale. All we need to ensure at this stage is that you cannot migrate a VM that has seen this to a host that doesn't have the feature. And if anything, this sort of selection should be defined by writing to the ID_AA64MMFR3_EL1 register from userspace and let the whole thing be driven by it. See Jing's current effort at [1]. Thanks, M. [1] https://lore.kernel.org/r/20230228062246.1222387-1-jingzhangos@google.com -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel