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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 4E542C28CC5 for ; Wed, 5 Jun 2019 12:19:07 +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 2658C206BA for ; Wed, 5 Jun 2019 12:19:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2658C206BA 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 DB9F3B50; Wed, 5 Jun 2019 12:19:06 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 58E4E9BA for ; Wed, 5 Jun 2019 12:19:05 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id EE5B634F for ; Wed, 5 Jun 2019 12:19:04 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 993C180D; Wed, 5 Jun 2019 05:19:04 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CC1EB3F246; Wed, 5 Jun 2019 05:19:02 -0700 (PDT) Date: Wed, 5 Jun 2019 13:19:00 +0100 From: Will Deacon To: Marc Gonzalez , joro@8bytes.org Subject: Re: [PATCH v3] iommu/arm-smmu: Avoid constant zero in TLBI writes Message-ID: <20190605121900.GJ15030@fuggles.cambridge.arm.com> References: <20190529130559.GB11023@fuggles.cambridge.arm.com> <84791515-e0ae-0322-78aa-02ca0b40d157@free.fr> <09a290f1-27a0-5ee3-16b9-659ef2ba99dc@free.fr> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <09a290f1-27a0-5ee3-16b9-659ef2ba99dc@free.fr> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () Cc: Jeffrey Hugo , MSM , Bjorn Andersson , iommu , Andy Gross , AngeloGioacchino Del Regno , Robin Murphy , Linux ARM 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org [+Joerg on To:] On Mon, Jun 03, 2019 at 02:15:37PM +0200, Marc Gonzalez wrote: > From: Robin Murphy > > Apparently, some Qualcomm arm64 platforms which appear to expose their > SMMU global register space are still, in fact, using a hypervisor to > mediate it by trapping and emulating register accesses. Sadly, some > deployed versions of said trapping code have bugs wherein they go > horribly wrong for stores using r31 (i.e. XZR/WZR) as the source > register. > > While this can be mitigated for GCC today by tweaking the constraints > for the implementation of writel_relaxed(), to avoid any potential > arms race with future compilers more aggressively optimising register > allocation, the simple way is to just remove all the problematic > constant zeros. For the write-only TLB operations, the actual value is > irrelevant anyway and any old nearby variable will provide a suitable > GPR to encode. The one point at which we really do need a zero to clear > a context bank happens before any of the TLB maintenance where crashes > have been reported, so is apparently not a problem... :/ > > Reported-by: AngeloGioacchino Del Regno > Tested-by: Marc Gonzalez > Signed-off-by: Robin Murphy > Signed-off-by: Marc Gonzalez Acked-by: Will Deacon Joerg -- Please can you take this as a fix for 5.2, with a Cc stable? Cheers, Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu