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,URIBL_BLOCKED,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 05DF4CA9EB5 for ; Mon, 4 Nov 2019 19:12:19 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 C844920848 for ; Mon, 4 Nov 2019 19:12:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C844920848 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 9D73FEF5; Mon, 4 Nov 2019 19:12:18 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 9C0DDCDB for ; Mon, 4 Nov 2019 19:12:16 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 00071710 for ; Mon, 4 Nov 2019 19:12:15 +0000 (UTC) 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 67DF41F1; Mon, 4 Nov 2019 11:12:15 -0800 (PST) Received: from [10.1.196.37] (e121345-lin.cambridge.arm.com [10.1.196.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C83AE3F71A; Mon, 4 Nov 2019 11:12:14 -0800 (PST) Subject: Re: [PATCH v2 08/10] iommu/io-pgtable-arm: Rationalise TTBRn handling To: Will Deacon References: <74ada0e6c488a2310206a553eb108cc28fd52457.1572024120.git.robin.murphy@arm.com> <5324d888-857a-b07c-439c-4ae4ea3a9784@arm.com> <20191104183655.GH24909@willie-the-truck> From: Robin Murphy Message-ID: <55865de4-1536-ed27-f5b5-aef188452ee5@arm.com> Date: Mon, 4 Nov 2019 19:12:13 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191104183655.GH24909@willie-the-truck> Content-Language: en-GB Cc: iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, Steven Price X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On 04/11/2019 18:36, Will Deacon wrote: > On Mon, Oct 28, 2019 at 06:51:55PM +0000, Robin Murphy wrote: >> On 28/10/2019 15:09, Steven Price wrote: >> [...] >>>> --- a/drivers/iommu/io-pgtable-arm-v7s.c >>>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c >>>> @@ -822,15 +822,13 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg, >>>> /* Ensure the empty pgd is visible before any actual TTBR write */ >>>> wmb(); >>>> - /* TTBRs */ >>>> - cfg->arm_v7s_cfg.ttbr[0] = virt_to_phys(data->pgd) | >>>> - ARM_V7S_TTBR_S | ARM_V7S_TTBR_NOS | >>>> - (cfg->coherent_walk ? >>>> - (ARM_V7S_TTBR_IRGN_ATTR(ARM_V7S_RGN_WBWA) | >>>> - ARM_V7S_TTBR_ORGN_ATTR(ARM_V7S_RGN_WBWA)) : >>>> - (ARM_V7S_TTBR_IRGN_ATTR(ARM_V7S_RGN_NC) | >>>> - ARM_V7S_TTBR_ORGN_ATTR(ARM_V7S_RGN_NC))); >>>> - cfg->arm_v7s_cfg.ttbr[1] = 0; >>>> + /* TTBR */ >>>> + cfg->arm_v7s_cfg.ttbr = virt_to_phys(data->pgd) | ARM_V7S_TTBR_S | >>>> + (cfg->coherent_walk ? (ARM_V7S_TTBR_NOS | >>>> + ARM_V7S_TTBR_IRGN_ATTR(ARM_V7S_RGN_WBWA) | >>>> + ARM_V7S_TTBR_ORGN_ATTR(ARM_V7S_RGN_WBWA)) : >>>> + (ARM_V7S_TTBR_IRGN_ATTR(ARM_V7S_RGN_NC) | >>>> + ARM_V7S_TTBR_ORGN_ATTR(ARM_V7S_RGN_NC))); >>> >>> ARM_V7S_TTBR_NOS seems to have sneaked into the cfg->coherent_walk >>> condition here - which you haven't mentioned in the commit log, so it >>> doesn't look like it should be in this commit. >> >> Ah, yes, it's taken a while to remember whether this was something important >> that got muddled up in rebasing, but it's actually just trivial cleanup. For >> !coherent_walk, the non-cacheable output attribute makes shareable accesses >> implicitly outer-shareable, so setting TTBR.NOS for that case actually does >> nothing except look misleading. Thus this is essentially just a cosmetic >> change included in the reformatting for clarity and consistency with the >> LPAE version. I'll call that out in the commit message, thanks for spotting! > > I vaguely remember a case where you had to mark non-cacheable accesses as > outer-shareable explicitly to avoid unpredictable behaviour. Hmm. > > /me looks at the Arm ARM > > Ok, it looks like this changed between ARMv7 and ARMv8. The ARMv7 ARM > states: > > | A memory region with a resultant memory type attribute of Normal, and a > | resultant cacheability attribute of Inner Non-cacheable, Outer > | Non-cacheable, must have a resultant shareability attribute of Outer > | Shareable, otherwise shareability is UNPREDICTABLE. > Although, SMMUv2 does go a bit further in saying: "In SMMUv2, the SMMU treats final attributes that are Normal Inner Non-cacheable or Normal Outer Non-cacheable as Outer Shareable. In SMMUv1, it is IMPLEMENTATION DEFINED how the SMMU treats such attributes." and SMMUv3 follows similar lines: "The SMMU does not output inconsistent attributes as a result of misconfiguration. Outer Shareable is used as the effective Shareability when Device or Normal Inner Non-cacheable Outer Non-cacheable types are configured." > Although this only seems to be the case for LPAE! The short descriptor docs are > less clear, but I think it might be wise to ensure that non-cacheable mappings > are always outer-shareable for consistency. Agreed, despite the above I think it does make sense to be explicit and not rely on subtleties. Between 9e6ea59f3ff3 and this patch we should have walks covered, so I can spin a followup to fix actual mappings as well. Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu