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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 0B96DC433E1 for ; Mon, 15 Jun 2020 14:18:13 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D295320644 for ; Mon, 15 Jun 2020 14:18:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="PMnKuz7H" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D295320644 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=fiCblKAHjWfO9Csp4ST//A5l01hMajNN1l9AJ0bCY5U=; b=PMnKuz7HPnDLsT ftsRn6xJxjhpT6tuAi/OsJW3LgToLL2vBvNdVjLKVQL8uevBC+WhKcyoyobz//fvzHNZr5yQlPgdF IR1hECG2TFDSTXjTKe0PUHUtOS7Ey/b0d2qgORty1xG3sz6jLc8Wn3sthIpbX4GvhBZOtBMmIR8WA k9wBK/WCYnqnvj3VzLMBeaHOG2T7W6t8dburZlgQTeOPLzRQv08t/30GvMlmxvPV/0P02NebsA6Eu CkVoDsLeIx0kUn43r+4hAilekvS1jrSQ1DKPkToDePbD3UDPZM+FqlITHhThyC+8JH59bK4TGtOW1 5MyCuulV8e2gGI34SI/w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jkpw9-0007he-NA; Mon, 15 Jun 2020 14:18:09 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jkpw0-0007Z9-6j for linux-arm-kernel@lists.infradead.org; Mon, 15 Jun 2020 14:18:01 +0000 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 DB5BC31B; Mon, 15 Jun 2020 07:17:58 -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 1CA6A3F6CF; Mon, 15 Jun 2020 07:17:58 -0700 (PDT) Date: Mon, 15 Jun 2020 15:17:56 +0100 From: Dave Martin To: Marc Zyngier Subject: Re: [PATCH 0/4] KVM/arm64: Enable PtrAuth on non-VHE KVM Message-ID: <20200615141755.GK25945@arm.com> References: <20200615081954.6233-1-maz@kernel.org> <20200615125920.GJ25945@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200615_071800_307635_30719662 X-CRM114-Status: GOOD ( 22.93 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel-team@android.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jun 15, 2020 at 02:22:19PM +0100, Marc Zyngier wrote: > Hi Dave, > > On 2020-06-15 13:59, Dave Martin wrote: > >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? > > Depending on the use case, very. See below. > > >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). > > Part of the work happening around running protected VMs (which cannot > be tampered with from EL1/0 host) makes it mandatory to disable VHE, > so that we can wrap the host EL1 in its own Stage-2 page tables. > We (the Android kernel team) are actively working on enabling this > feature. > > >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'm all for having VHE on for platforms that support it. Which is why > CONFIG_VHE=y is present in defconfig. However, we cannot offer the same > level of guarantee as we can hopefully achieve with non-VHE (we can > drop mappings from Stage-1, but can't protect VMs from an evil or > compromised host). This is a very different use case from the usual > "reduced hypervisor overhead" that we want in the general case. > > >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. > > It is a concern. I guess that if we manage to get some traction on > Android, then the feature will get some testing! And yes, SVE is > next on my list. > > >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... > > I think having started with a slightly smaller problem space was the > right thing to do at the time. We are now reasonably confident that > KVM and SVE are working correctly together, and we can now try to enable > it on !VHE. Cool, now I understand. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel