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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7CF23C47253 for ; Fri, 1 May 2020 10:37:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 60B7D206B8 for ; Fri, 1 May 2020 10:37:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728618AbgEAKhX (ORCPT ); Fri, 1 May 2020 06:37:23 -0400 Received: from foss.arm.com ([217.140.110.172]:38456 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728545AbgEAKhX (ORCPT ); Fri, 1 May 2020 06:37:23 -0400 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 7BA4F30E; Fri, 1 May 2020 03:37:22 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.7.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8266F3F73D; Fri, 1 May 2020 03:37:20 -0700 (PDT) Date: Fri, 1 May 2020 11:37:12 +0100 From: Mark Rutland To: Greg KH Cc: Jeremy Linton , linux-usb@vger.kernel.org, stern@rowland.harvard.edu, git@thegavinli.com, jarkko.sakkinen@linux.intel.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] usb: usbfs: correct kernel->user page attribute mismatch Message-ID: <20200501103712.GA51954@C02TD0UTHF1T.local> References: <20200430211922.929165-1-jeremy.linton@arm.com> <20200501070500.GA887524@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200501070500.GA887524@kroah.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 01, 2020 at 09:05:00AM +0200, Greg KH wrote: > On Thu, Apr 30, 2020 at 04:19:22PM -0500, Jeremy Linton wrote: > > On arm64, and possibly other architectures, requesting > > IO coherent memory may return Normal-NC if the underlying > > hardware isn't coherent. If these pages are then > > remapped into userspace as Normal, that defeats the > > purpose of getting Normal-NC, as well as resulting in > > mappings with differing cache attributes. > > What is "Normal-NC"? Arm terminology for "Normal Non-Cacheable"; it might be better to say something like: On some architectures (e.g. arm64) an IO coherent mapping may use non-cachable attributes if the relevant device is cache coherent. If userspace mappings are cacheable, these may not be coherent with non-cacheable mappings. On arm64 this is the case for Normal-NC and Normal (cacheable) mappings. Thanks, Mark.