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 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 AA7DAC43381 for ; Thu, 14 Feb 2019 11:03:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 746E0222B6 for ; Thu, 14 Feb 2019 11:03:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2438462AbfBNLD1 (ORCPT ); Thu, 14 Feb 2019 06:03:27 -0500 Received: from foss.arm.com ([217.140.101.70]:41494 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725835AbfBNLD1 (ORCPT ); Thu, 14 Feb 2019 06:03:27 -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 E54D5EBD; Thu, 14 Feb 2019 03:03:26 -0800 (PST) Received: from [10.162.0.144] (a075553-lin.blr.arm.com [10.162.0.144]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9542B3F575; Thu, 14 Feb 2019 03:03:23 -0800 (PST) Subject: Re: [PATCH v5 2/5] arm64/kvm: preserve host HCR_EL2/MDCR_EL2 value To: Kristina Martsenko , 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 References: <1548658727-14271-1-git-send-email-amit.kachhap@arm.com> <1548658727-14271-3-git-send-email-amit.kachhap@arm.com> <8de32a89-4aa1-bffb-78dd-45feddc9216e@arm.com> From: Amit Daniel Kachhap Message-ID: <1a2534b9-6d3b-caac-ff05-7795b7a2d725@arm.com> Date: Thu, 14 Feb 2019 16:33:21 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <8de32a89-4aa1-bffb-78dd-45feddc9216e@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed 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 Hi, On 2/13/19 11:04 PM, Kristina Martsenko wrote: > On 28/01/2019 06:58, Amit Daniel Kachhap wrote: >> When restoring HCR_EL2 for the host, KVM uses HCR_HOST_VHE_FLAGS, which >> is a constant value. This works today, as the host HCR_EL2 value is >> always the same, but this will get in the way of supporting extensions >> that require HCR_EL2 bits to be set conditionally for the host. >> >> To allow such features to work without KVM having to explicitly handle >> every possible host feature combination, this patch has KVM save/restore >> the host HCR when switching to/from a guest HCR. The saving of the >> register is done once during cpu hypervisor initialization state and is >> just restored after switch from guest. > > Why is this patch needed? I couldn't find anything in this series that > sets HCR_EL2 conditionally for the host. It seems like the kernel still > always sets it to HCR_HOST_VHE_FLAGS/HCR_HOST_NVHE_FLAGS. This patch is not directly related to pointer authentication but just a helper to optimize save/restore. In this way save may be avoided for each switch and only restore is done. Patch 3 does sets HCR_EL2 in VHE_RUN. > > Looking back at v2 of the userspace pointer auth series, it seems that > the API/APK bits were set conditionally [1], so this patch would have > been needed to preserve HCR_EL2. But as of v3 of that series, the bits > have been set unconditionally through HCR_HOST_NVHE_FLAGS [2]. > > Is there something else I've missed? Now HCR_EL2 is modified during switch time and NHVE doesnt support ptrauth so [2] doesn't makes sense. //Amit D > > Thanks, > Kristina > > [1] https://lore.kernel.org/linux-arm-kernel/20171127163806.31435-6-mark.rutland@arm.com/ > [2] https://lore.kernel.org/linux-arm-kernel/20180417183735.56985-5-mark.rutland@arm.com/ >