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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 6C710C43381 for ; Wed, 20 Mar 2019 15:04:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 404AC2184E for ; Wed, 20 Mar 2019 15:04:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728354AbfCTPEU (ORCPT ); Wed, 20 Mar 2019 11:04:20 -0400 Received: from foss.arm.com ([217.140.101.70]:41634 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727469AbfCTPET (ORCPT ); Wed, 20 Mar 2019 11:04:19 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0D425174E; Wed, 20 Mar 2019 08:04:19 -0700 (PDT) Received: from [10.1.197.21] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C9F223F740; Wed, 20 Mar 2019 08:04:16 -0700 (PDT) Subject: Re: [PATCH v7 9/10] KVM: arm64: docs: document KVM support of pointer authentication To: Julien Thierry , Amit Daniel Kachhap , linux-arm-kernel@lists.infradead.org Cc: Christoffer Dall , Marc Zyngier , Catalin Marinas , Will Deacon , Andrew Jones , Dave Martin , Ramana Radhakrishnan , kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Mark Rutland , James Morse References: <1552984243-7689-1-git-send-email-amit.kachhap@arm.com> <1552984243-7689-10-git-send-email-amit.kachhap@arm.com> <7bf19035-02ba-ae47-b08c-7d7622a45dbf@arm.com> From: Kristina Martsenko Message-ID: <648d66dd-519c-7567-a3e1-c23208f68cf2@arm.com> Date: Wed, 20 Mar 2019 15:04:15 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <7bf19035-02ba-ae47-b08c-7d7622a45dbf@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/03/2019 13:37, Julien Thierry wrote: > Hi Amit, > > On 19/03/2019 08:30, Amit Daniel Kachhap wrote: >> This adds sections for KVM API extension for pointer authentication. >> A brief description about usage of pointer authentication for KVM guests >> is added in the arm64 documentations. [...] >> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt >> index 7de9eee..b5c66bc 100644 >> --- a/Documentation/virtual/kvm/api.txt >> +++ b/Documentation/virtual/kvm/api.txt >> @@ -2659,6 +2659,12 @@ Possible features: >> Depends on KVM_CAP_ARM_PSCI_0_2. >> - KVM_ARM_VCPU_PMU_V3: Emulate PMUv3 for the CPU. >> Depends on KVM_CAP_ARM_PMU_V3. >> + - KVM_ARM_VCPU_PTRAUTH_ADDRESS: >> + - KVM_ARM_VCPU_PTRAUTH_GENERIC: >> + Enables Pointer authentication for the CPU. >> + Depends on KVM_CAP_ARM_PTRAUTH and only on arm64 architecture. If >> + set, then the KVM guest allows the execution of pointer authentication >> + instructions. Otherwise, KVM treats these instructions as undefined. >> > > Overall I feel one could easily get confused to whether > PTRAUTH_ADDRESS/GENERIC are two individual features, whether one is a > superset of the other, if the names are just an alias of one another, etc... > > I think the doc should at least stress out that *both* flags are > required to enable ptrauth in a guest. However it raises the question, > if we don't plan to support the features individually (because we > can't), should we really expose two feature flags? I seems odd to > introduce two flags that only do something if used together... Why can't we support the features individually? For example, if we ever get a system where all CPUs support address authentication and none of them support generic authentication, then we could still support address authentication in the guest. Thanks, Kristina