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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 5FC44C43441 for ; Fri, 23 Nov 2018 10:49:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F2EE206B2 for ; Fri, 23 Nov 2018 10:49:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F2EE206B2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-parisc-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409486AbeKWVdG (ORCPT ); Fri, 23 Nov 2018 16:33:06 -0500 Received: from 8bytes.org ([81.169.241.247]:49232 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387655AbeKWVdG (ORCPT ); Fri, 23 Nov 2018 16:33:06 -0500 Received: by theia.8bytes.org (Postfix, from userid 1000) id 7EE16322; Fri, 23 Nov 2018 11:49:18 +0100 (CET) Date: Fri, 23 Nov 2018 11:49:18 +0100 From: Joerg Roedel To: Robin Murphy Cc: Linus Torvalds , linux@armlinux.org.uk, Christoph Hellwig , linux-arch@vger.kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, David Woodhouse , the arch/x86 maintainers , Linux List Kernel Mailing , iommu@lists.linux-foundation.org, jdmason@kudzu.us, xen-devel@lists.xenproject.org, linux-arm-kernel@lists.infradead.org, m.szyprowski@samsung.com Subject: Re: remove the ->mapping_error method from dma_map_ops V2 Message-ID: <20181123104918.GE1586@8bytes.org> References: <20181122140320.24080-1-hch@lst.de> <20181122170715.GI30658@n2100.armlinux.org.uk> <11829e3c-7302-f821-cf5c-863e5267a17b@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <11829e3c-7302-f821-cf5c-863e5267a17b@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On Thu, Nov 22, 2018 at 05:52:15PM +0000, Robin Murphy wrote: > Unfortunately, with things like the top-down IOVA allocator, and 32-bit > systems in general, "the top 4095" values may well still be valid addresses > - we're relying on a 1-byte mapping of the very top byte of memory/IOVA > space being sufficiently ridiculous that no real code would ever do that, > but even a 4-byte mapping of the top 4 bytes is within the realms of the > plausible (I've definitely seen the USB layer make 8-byte mappings from any > old offset within a page, for example). But we can easily work around that by reserving the top 4k of the first 4GB of IOVA address space in the allocator, no? Then these values are never returned as valid DMA handles. Regards, Joerg