From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751963AbcDUIfZ (ORCPT ); Thu, 21 Apr 2016 04:35:25 -0400 Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:39520 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751228AbcDUIfX (ORCPT ); Thu, 21 Apr 2016 04:35:23 -0400 Date: Thu, 21 Apr 2016 09:35:12 +0100 From: One Thousand Gnomes To: Nicolas Morey-Chaisemartin Cc: linux-kernel@vger.kernel.org Subject: Re: [Question] Missing data after DMA read transfer Message-ID: <20160421093512.4a63e2c2@lxorguk.ukuu.org.uk> In-Reply-To: <0ae37751-a824-7ac7-6723-66142d5d861c@kalray.eu> References: <0ae37751-a824-7ac7-6723-66142d5d861c@kalray.eu> Organization: Intel Corporation X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > 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