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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 83DB6C433E1 for ; Thu, 21 May 2020 02:26:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2C61B20748 for ; Thu, 21 May 2020 02:26:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ifaeD5kr" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2C61B20748 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8EE2D80008; Wed, 20 May 2020 22:26:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 89FB280007; Wed, 20 May 2020 22:26:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7B63380008; Wed, 20 May 2020 22:26:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0136.hostedemail.com [216.40.44.136]) by kanga.kvack.org (Postfix) with ESMTP id 62CD080007 for ; Wed, 20 May 2020 22:26:42 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 22243181AEF21 for ; Thu, 21 May 2020 02:26:42 +0000 (UTC) X-FDA: 76839137844.20.hand98_46b18fe7f22 X-HE-Tag: hand98_46b18fe7f22 X-Filterd-Recvd-Size: 3088 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Thu, 21 May 2020 02:26:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=AQAUQIhz6SqBbHGlDEdDO7YRyc583EZtNH+fi0JhOnE=; b=ifaeD5kroRd/pg4bLz7jN/XLLB 24s4q/bsYF++8aYyezv8cokcKu+WD/hZrpLUbHTlKnTjD6hW74FM8TrnKUbeFGn4eFyM45w4IKXyx ezbJjWLew8N86eaP2nowALIAff5ceiTIWylAWtiW763IPK0l+62dxzIfbpgofkuiGe/xZ7BzR+ch2 MA8+mG00jCMq8151XmnIzj+YKevgflB27ZShQL0Fw2HIU0kgJWg492JPECQmnRYdhFeA0JGNLzS8Y AM5hzNtriG8TRn1NwAxUdL2Ak7EI2CeDCA0mOGlRyBiKgRGjaZzuXmOWN4eIleMLAPAebHkmiiNrG xYzANe4A==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbaui-0003R9-PO; Thu, 21 May 2020 02:26:28 +0000 Date: Wed, 20 May 2020 19:26:28 -0700 From: Matthew Wilcox To: Dan Williams Cc: gregkh@linuxfoundation.org, Arnd Bergmann , Ingo Molnar , Kees Cook , Russell King , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3] /dev/mem: Revoke mappings when a driver claims the region Message-ID: <20200521022628.GE16070@bombadil.infradead.org> References: <159002475918.686697.11844615159862491335.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <159002475918.686697.11844615159862491335.stgit@dwillia2-desk3.amr.corp.intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 20, 2020 at 06:35:25PM -0700, Dan Williams wrote: > +static struct inode *devmem_inode; > + > +#ifdef CONFIG_IO_STRICT_DEVMEM > +void revoke_devmem(struct resource *res) > +{ > + struct inode *inode = READ_ONCE(devmem_inode); > + > + /* > + * Check that the initialization has completed. Losing the race > + * is ok because it means drivers are claiming resources before > + * the fs_initcall level of init and prevent /dev/mem from > + * establishing mappings. > + */ > + smp_rmb(); > + if (!inode) > + return; But we don't need the smp_rmb() here, right? READ_ONCE and WRITE_ONCE are a DATA DEPENDENCY barrier (in Documentation/memory-barriers.txt parlance) so the smp_rmb() is superfluous ... > + /* > + * Use a unified address space to have a single point to manage > + * revocations when drivers want to take over a /dev/mem mapped > + * range. > + */ > + inode->i_mapping = devmem_inode->i_mapping; > + inode->i_mapping->host = devmem_inode; umm ... devmem_inode->i_mapping->host doesn't already point to devmem_inode? > + > + /* publish /dev/mem initialized */ > + smp_wmb(); > + WRITE_ONCE(devmem_inode, inode); As above, unnecessary barrier, I think.