From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E2D1A2EB10; Thu, 16 May 2024 07:48:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715845720; cv=none; b=IM7gPUOG4xioYPH6hmu+naZD3FbvD6sRoqtxb15/D1edwPOA8bClFv/MoR3Nugoe04gFo5fRg4QnbGSWvhoDocqeYyNnD5sGbGG91mxUamv1saf9xZM/KjXwiy585pebNtleQZ+mtbhQFMTmUDUxze/X1bwKfOfk+8YQhpd0ipg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715845720; c=relaxed/simple; bh=T4oOZ1LmeWclvKPglpSa/G3iKDDHJ/ls07wv3wVQ2EA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fCfYru8rA1osYyQngV4iyQF1QlOqFJsEl6P1hNu9PIi7Qa3T8qquMgVSewkPU0BgC+FojIdcsYAbrUy2nfhf1DpWWNxupGSTcOZljQx+OWxhdpUfOVKsLuxk8HY9y/voSZDvmYaGGTmCJvV/mJn7LbGRuHWa4TZPSxvrOSJA5I4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F562C113CC; Thu, 16 May 2024 07:48:36 +0000 (UTC) Date: Thu, 16 May 2024 08:48:34 +0100 From: Catalin Marinas To: Suzuki K Poulose Cc: Steven Price , kvm@vger.kernel.org, kvmarm@lists.linux.dev, Marc Zyngier , Will Deacon , James Morse , Oliver Upton , Zenghui Yu , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Joey Gouly , Alexandru Elisei , Christoffer Dall , Fuad Tabba , linux-coco@lists.linux.dev, Ganapatrao Kulkarni Subject: Re: [PATCH v2 09/14] arm64: Enable memory encrypt for Realms Message-ID: References: <20240412084213.1733764-1-steven.price@arm.com> <20240412084213.1733764-10-steven.price@arm.com> <5b2db977-7f0f-4c3a-b278-f195c7ddbd80@arm.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5b2db977-7f0f-4c3a-b278-f195c7ddbd80@arm.com> On Wed, May 15, 2024 at 11:47:02AM +0100, Suzuki K Poulose wrote: > On 14/05/2024 19:00, Catalin Marinas wrote: > > On Fri, Apr 12, 2024 at 09:42:08AM +0100, Steven Price wrote: > > Can someone summarise what the point of this protection bit is? The IPA > > memory is marked as protected/unprotected already via the RSI call and > > presumably the RMM disables/permits sharing with a non-secure hypervisor > > accordingly irrespective of which alias the realm guest has the linear > > mapping mapped to. What does it do with the top bit of the IPA? Is it > > that the RMM will prevent (via Stage 2) access if the IPA does not match > > the requested protection? IOW, it unmaps one or the other at Stage 2? > > The Realm's IPA space is split in half. The lower half is "protected" > and all pages backing the "protected" IPA is in the Realm world and > thus cannot be shared with the hypervisor. The upper half IPA is > "unprotected" (backed by Non-secure PAS pages) and can be accessed > by the Host/hyp. What about emulated device I/O where there's no backing RAM at an IPA. Does it need to have the top bit set? > The RSI call (RSI_IPA_STATE_SET) doesn't make an IPA unprotected. It > simply "invalidates" a (protected) IPA to "EMPTY" implying the Realm doesn't > intend to use the "ipa" as RAM anymore and any access to it from > the Realm would trigger an SEA into the Realm. The RSI call triggers an exit > to the host with the information and is a hint to the hypervisor to reclaim > the page backing the IPA. > > Now, given we need dynamic "sharing" of pages (instead of a dedicated > set of shared pages), "aliasing" of an IPA gives us shared pages. > i.e., If OS wants to share a page "x" (protected IPA) with the host, > we mark that as EMPTY via RSI call and then access the "x" with top-bit > set (aliasing the IPA x). This fault allows the hyp to map the page backing > IPA "x" as "unprotected" at ALIAS(x) address. Does the RMM sanity-checks that the NS hyp mappings are protected or unprotected depending on the IPA range? I assume that's also the case if the NS hyp is the first one to access a page before the realm (e.g. inbound virtio transfer; no page allocated yet because of a realm access). -- Catalin