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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23D12CDB47E for ; Fri, 13 Oct 2023 15:28:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232413AbjJMP2V (ORCPT ); Fri, 13 Oct 2023 11:28:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232383AbjJMP2T (ORCPT ); Fri, 13 Oct 2023 11:28:19 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE82FDE for ; Fri, 13 Oct 2023 08:28:17 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E84CC433C8; Fri, 13 Oct 2023 15:28:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697210897; bh=iiew/laD+Q3haHwMxgaUmOJOpF//XuI1aJ4hOlOKh6s=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=B6aOhjI4W3T3qqRBW/NsttzXu5HUYLUV0lP13HpcxULbCsY8haM+fvx/hkj6ifjtz 5uZCpSp2yYae/IoUGpnXO1b3PAiCRuxJ2QNmSgt762IP05AQmV1jLJKNvfC3fo3Nff Z1eyDfRCPYIEucr4zoADjXI4vRzVrqegikLNsl094KykJc8hZMs9isjWNn37ugG4mL b7BS7rV1TDFjqx3xH9xB/2V45Bkqj8K5qirF/WyXBzb1dv9lhsMC7rfYLnjJAqVQfh xNspCeaor9aeIXP83je9bdwKF47wno/dy555mpvKuCdCi1hRXBYmhqlW+lJOw1Ar8m CQCLt2ppkzeJA== Date: Fri, 13 Oct 2023 17:28:10 +0200 From: Lorenzo Pieralisi To: Catalin Marinas Cc: Will Deacon , Jason Gunthorpe , ankita@nvidia.com, maz@kernel.org, oliver.upton@linux.dev, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 2/2] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory Message-ID: References: <20231012123541.GB11824@willie-the-truck> <20231012144807.GA12374@willie-the-truck> <20231013092934.GA13524@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 13, 2023 at 02:08:10PM +0100, Catalin Marinas wrote: [...] > Yes, we end up with mismatched aliases but they only matter if the VMM > also accesses the I/O range via its own mapping. So far I haven't seen > case that suggests this. > > > > Things can go wrong but that's not because Device does anything better. > > > Given the RAS implementation, external aborts caused on Device memory > > > (e.g. wrong size access) is uncontainable. For Normal NC it can be > > > contained (I can dig out the reasoning behind this if you want, IIUC > > > something to do with not being able to cancel an already issued Device > > > access since such accesses don't allow speculation due to side-effects; > > > for Normal NC, it's just about the software not getting the data). > > > > I really think these details belong in the commit message. > > I guess another task for Lorenzo ;). I will do, I start wondering though whether this documentation belongs in this commit log only or at Documentation/arch/arm64 level (or both), I am pretty sure this thread can turn out quite useful as a reference (it is for me) if we manage to summarize it that would benefit everyone. Lorenzo