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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 CF528C169C4 for ; Thu, 31 Jan 2019 16:19:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A05532085B for ; Thu, 31 Jan 2019 16:19:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388266AbfAaQTk (ORCPT ); Thu, 31 Jan 2019 11:19:40 -0500 Received: from foss.arm.com ([217.140.101.70]:47142 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731284AbfAaQTj (ORCPT ); Thu, 31 Jan 2019 11:19:39 -0500 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 22C3A80D; Thu, 31 Jan 2019 08:19:39 -0800 (PST) Received: from [10.1.196.105] (eglon.cambridge.arm.com [10.1.196.105]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 759CB3F557; Thu, 31 Jan 2019 08:19:37 -0800 (PST) Subject: Re: [PATCH v4 3/6] arm64/kvm: add a userspace option to enable pointer authentication To: Amit Daniel Kachhap Cc: LAK , Marc Zyngier , Catalin Marinas , Will Deacon , Kristina Martsenko , kvmarm@lists.cs.columbia.edu, Ramana Radhakrishnan , Dave Martin , linux-kernel@vger.kernel.org References: <1545119810-12182-1-git-send-email-amit.kachhap@arm.com> <1545119810-12182-4-git-send-email-amit.kachhap@arm.com> <49474d5f-6f4e-b57d-4b45-94c16d85136c@arm.com> From: James Morse Message-ID: <3936d9fd-1e3f-0437-e866-edf2d9cbf797@arm.com> Date: Thu, 31 Jan 2019 16:19:35 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Amit, On 09/01/2019 10:13, Amit Daniel Kachhap wrote: > On Sat, Jan 5, 2019 at 12:05 AM James Morse wrote: >> On 18/12/2018 07:56, Amit Daniel Kachhap wrote: >>> This feature will allow the KVM guest to allow the handling of >>> pointer authentication instructions or to treat them as undefined >>> if not set. It uses the existing vcpu API KVM_ARM_VCPU_INIT to >>> supply this parameter instead of creating a new API. >>> >>> A new register is not created to pass this parameter via >>> SET/GET_ONE_REG interface as just a flag (KVM_ARM_VCPU_PTRAUTH) >>> supplied is enough to select this feature. >> >> What is the motivation for doing this? Doesn't ptrauth 'just' need turning on? >> It doesn't need additional setup to be useable, or rely on some qemu support to >> work properly. There isn't any hidden state that can't be migrated in the usual way. >> Is it just because we don't want to commit to the ABI? > This allows migration of guest to non pointer authenticated supported > systems and hides the extra ptrauth registers. The MIDR already has to match, so the hardware must be the same. I guess this lets us hide the new feature so old-guests can migrate to a new-kernel without a write to the id registers failing. > Basically this suggestion was given by Christoffer > (https://lore.kernel.org/lkml/20180206123847.GY21802@cbox/). Ah, Christoffer asked for it, that's reason enough! Thanks, James