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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 318ECC388F2 for ; Fri, 6 Nov 2020 09:57:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD0B722202 for ; Fri, 6 Nov 2020 09:57:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604656628; bh=7k+t6D9+wpCTXBdefzDfDbiTH2zQDjta8PTrfd8tDa0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=AimkPpvYLdXn9EZUMrWyQ1GkFglm9k7fWh5Lh5bY+6KMqptkP3JNdG2k/IK39tVag 2n8MbSx6ZQ8qGL4/6Er7H7kX+/JIGu3+tS/dZGbBXRezAqjaTHFt6fyCYyU/3L7WXD inEkXWE17hoq+z5Qci/HpgNkUJtmGsUqEzgABVX8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726621AbgKFJ5H (ORCPT ); Fri, 6 Nov 2020 04:57:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:39046 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726075AbgKFJ5H (ORCPT ); Fri, 6 Nov 2020 04:57:07 -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 E108B20B80; Fri, 6 Nov 2020 09:57:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604656627; bh=7k+t6D9+wpCTXBdefzDfDbiTH2zQDjta8PTrfd8tDa0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=nlvr1Tz1wWGJ1mgrgtClOUmilBn7fgUtvjxfmP49knvor83tz0AID5fpC/e10x3Na 5fA2yUfgqMKrIMuoafHLqiXDsvLNB1rqknB1iEHYh3GssE78engknOQAV8JEHvx3WC 50i3UEJibPtZ3FNpe3PTpWvSM0sYHc0xSF0MQUrY= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kayUS-00892a-Mm; Fri, 06 Nov 2020 09:57:04 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 06 Nov 2020 09:57:04 +0000 From: Marc Zyngier To: Will Deacon Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Peng Liang , James Morse , Julien Thierry , Suzuki K Poulose , kernel-team@android.com Subject: Re: [PATCH 1/3] KVM: arm64: Allow setting of ID_AA64PFR0_EL1.CSV2 from userspace In-Reply-To: <20201105224442.GD8842@willie-the-truck> References: <20201103171445.271195-1-maz@kernel.org> <20201103171445.271195-2-maz@kernel.org> <20201105224442.GD8842@willie-the-truck> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <32241e9ee49133df4e9bcc6c8ebd7551@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, liangpeng10@huawei.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@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 2020-11-05 22:44, Will Deacon wrote: >> + if (csv2 > vcpu->kvm->arch.pfr0_csv2) >> + return -EINVAL; >> + vcpu->kvm->arch.pfr0_csv2 = csv2; >> + >> + /* This is what we mean by invariant: you can't change it. */ >> + if (val != read_id_reg(vcpu, rd, false)) >> + return -EINVAL; > > I think it's quite confusing to return -EINVAL in the case that we have > actually updated arch.pfr0_csv2, as it's indistinguishable from the > case > when csv2 was invalid and the field wasn't updated. -EINVAL is the right error code here (you're setting an invalid value for the whole register). The bug is that we have now changed CSV2 for everyone. I'll have a look at fixing this, though it might involve some locking. M. -- Jazz is not dead. It just smells funny...