From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751650AbcDUIv6 (ORCPT ); Thu, 21 Apr 2016 04:51:58 -0400 Received: from zimbra1.kalray.eu ([92.103.151.219]:37837 "EHLO zimbra1.kalray.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751282AbcDUIvz convert rfc822-to-8bit (ORCPT ); Thu, 21 Apr 2016 04:51:55 -0400 DKIM-Filter: OpenDKIM Filter v2.9.2 zimbra1.kalray.eu 3D9C8281E2B Subject: Re: [Question] Missing data after DMA read transfer To: One Thousand Gnomes References: <0ae37751-a824-7ac7-6723-66142d5d861c@kalray.eu> <20160421093512.4a63e2c2@lxorguk.ukuu.org.uk> Cc: linux-kernel@vger.kernel.org From: Nicolas Morey-Chaisemartin Message-ID: <278aff83-5d3a-e755-a4c3-50bfccf08886@kalray.eu> Date: Thu, 21 Apr 2016 10:51:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <20160421093512.4a63e2c2@lxorguk.ukuu.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 04/21/2016 à 10:35 AM, One Thousand Gnomes a écrit : >> But if I try to copy_from_user (using the address coming from userland, the one passed to get_user_pages), the data has not been written and I see the memset value. >> >> I manage to build a test case that fails all the time, but never at the same offset within the buffer. >> It's always in the middle (never at the start nor end), for a few pages long (varies between runs). > Always page aligned, always cache line aligned or arbitrarily aligned ? > > Alan It's always page aligned for both start and end (meaning last "untransferred" byte is the last byte of a page) Nicolas