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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 5FE9EC433E0 for ; Mon, 15 Jun 2020 12:59:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3FB6B2076A for ; Mon, 15 Jun 2020 12:59:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730097AbgFOM7Z (ORCPT ); Mon, 15 Jun 2020 08:59:25 -0400 Received: from foss.arm.com ([217.140.110.172]:47210 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730070AbgFOM7Y (ORCPT ); Mon, 15 Jun 2020 08:59:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E334431B; Mon, 15 Jun 2020 05:59:23 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2461D3F6CF; Mon, 15 Jun 2020 05:59:23 -0700 (PDT) Date: Mon, 15 Jun 2020 13:59:21 +0100 From: Dave Martin To: Marc Zyngier Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com Subject: Re: [PATCH 0/4] KVM/arm64: Enable PtrAuth on non-VHE KVM Message-ID: <20200615125920.GJ25945@arm.com> References: <20200615081954.6233-1-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200615081954.6233-1-maz@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Jun 15, 2020 at 09:19:50AM +0100, Marc Zyngier wrote: > Not having PtrAuth on non-VHE KVM (for whatever reason VHE is not > enabled on a v8.3 system) has always looked like an oddity. This > trivial series remedies it, and allows a non-VHE KVM to offer PtrAuth > to its guests. How likely do you think it is that people will use such a configuration? The only reason I can see for people to build a kernel with CONFIG_VHE=n is as a workaround for broken hardware, or because the kernel is too old to support VHE (in which case it doesn't understand ptrauth either, so it is irrelevant whether ptrauth depends on VHE). I wonder whether it's therefore better to "encourage" people to turn VHE on by making subsequent features depend on it where appropriate. We do want multiplatform kernels to be configured with CONFIG_VHE=y for example. I ask this, because SVE suffers the same "oddity". If SVE can be enabled for non-VHE kernels straightforwardly then there's no reason not to do so, but I worried in the past that this would duplicate complex code that would never be tested or used. If supporting ptrauth with !VHE is as simple as this series suggests, then it's low-risk. Perhaps SVE isn't much worse. I was chasing nasty bugs around at the time the SVE KVM support was originally written, and didn't want to add more unknowns into the mix... (Note, this is not an offer from me to do the SVE work!) [...] Cheers ---Dave