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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7CFCEC54EBD for ; Fri, 13 Jan 2023 11:11:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241365AbjAMLLO (ORCPT ); Fri, 13 Jan 2023 06:11:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240712AbjAMLKY (ORCPT ); Fri, 13 Jan 2023 06:10:24 -0500 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 737C3777E2; Fri, 13 Jan 2023 03:01:12 -0800 (PST) Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4NtdfT4ckFz6H7Dt; Fri, 13 Jan 2023 18:57:21 +0800 (CST) Received: from localhost (10.81.201.219) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Fri, 13 Jan 2023 11:01:09 +0000 Date: Fri, 13 Jan 2023 11:01:08 +0000 From: Jonathan Cameron To: Fan Ni CC: "alison.schofield@intel.com" , "vishal.l.verma@intel.com" , "ira.weiny@intel.com" , "bwidawsk@kernel.org" , "dan.j.williams@intel.com" , "dan.carpenter@oracle.com" , "linux-cxl@vger.kernel.org" , Adam Manzanares , "dave@stgolabs.net" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] cxl/region: Fix null pointer dereference for resetting decoder Message-ID: <20230113110108.00002122@Huawei.com> In-Reply-To: <20221215170909.2650271-1-fan.ni@samsung.com> References: <20221215170909.2650271-1-fan.ni@samsung.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.81.201.219] X-ClientProxiedBy: lhrpeml100003.china.huawei.com (7.191.160.210) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 Dec 2022 17:09:14 +0000 Fan Ni wrote: > Not all decoders have a reset callback. > > The CXL specification allows a host bridge with a single root port to > have no explicit HDM decoders. Currently the region driver assumes there > are none. As such the CXL core creates a special pass through decoder > instance without a commit/reset callback. > > Prior to this patch, the ->reset() callback was called unconditionally when > calling cxl_region_decode_reset. Thus a configuration with 1 Host Bridge, > 1 Root Port, and one directly attached CXL type 3 device or multiple CXL > type 3 devices attached to downstream ports of a switch can cause a null > pointer dereference. > > Before the fix, a kernel crash was observed when we destroy the region, and > a pass through decoder is reset. > > The issue can be reproduced as below, > 1) create a region with a CXL setup which includes a HB with a > single root port under which a memdev is attached directly. > 2) destroy the region with cxl destroy-region regionX -f. > > Fixes: 176baefb2eb5 ("cxl/hdm: Commit decoder state to hardware") > Signed-off-by: Fan Ni Explanation seems correct to me. Only question (and it's one for the Maintainers) is whether they prefer optionality here or a stub reset() implementation for the pass through decoder. either way Reviewed-by: Jonathan Cameron > --- > drivers/cxl/core/region.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c > index f9ae5ad284ff..3931793a13ac 100644 > --- a/drivers/cxl/core/region.c > +++ b/drivers/cxl/core/region.c > @@ -131,7 +131,7 @@ static int cxl_region_decode_reset(struct cxl_region *cxlr, int count) > struct cxl_memdev *cxlmd = cxled_to_memdev(cxled); > struct cxl_port *iter = cxled_to_port(cxled); > struct cxl_ep *ep; > - int rc; > + int rc = 0; > > while (!is_cxl_root(to_cxl_port(iter->dev.parent))) > iter = to_cxl_port(iter->dev.parent); > @@ -143,7 +143,8 @@ static int cxl_region_decode_reset(struct cxl_region *cxlr, int count) > > cxl_rr = cxl_rr_load(iter, cxlr); > cxld = cxl_rr->decoder; > - rc = cxld->reset(cxld); > + if (cxld->reset) > + rc = cxld->reset(cxld); > if (rc) > return rc; > } > @@ -186,7 +187,8 @@ static int cxl_region_decode_commit(struct cxl_region *cxlr) > iter = ep->next, ep = cxl_ep_load(iter, cxlmd)) { > cxl_rr = cxl_rr_load(iter, cxlr); > cxld = cxl_rr->decoder; > - cxld->reset(cxld); > + if (cxld->reset) > + cxld->reset(cxld); > } > > cxled->cxld.reset(&cxled->cxld);