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Wed, 1 Feb 2023 08:24:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1675268681; bh=2bdI4TPDn3elYpB6pyzaj01gJj8K33x3qyWJhEoPEM8=; h=Date:From:To:Cc:Subject:Content-Type; b=Udzue+WIdmQOAtw7WDMz1KaYZmcXYFd6qamRuW7aQPDrtdWa4shS7pcl5orFfkVKJ GuhZ8gUO031w5RLJI8K7HMhU+TbMpPK+kJ18I2wpBJj2zEy5mCTv2kbjydDSEDKxXr IJu3TYdTBXbA8NhyqiX8rBH739c62xVrVw9q6ATkjttoqEQFMWeDeVrG1S9NpED7fx m2ohl51LHhUK/V57sb1r2jCsX4oJX3FAuzWH2uEc6Gldn0CrVf+AndPlgWG+z+mR/y Qw/3Esbdav7osvAx5PnkybLo4vJjiLuntt/LmqKTZ3gP3CU9NHqBFC6M6o3+wqiIn5 22V+0Kqw35iHg== Date: Wed, 1 Feb 2023 07:57:29 -0800 From: Davidlohr Bueso 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" , "Jonathan.Cameron@huawei.com" , "dan.carpenter@oracle.com" , "linux-cxl@vger.kernel.org" , Adam Manzanares , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] cxl/region: Fix null pointer dereference for resetting decoder Message-ID: <20230201155729.wnil24dijtd2rfhl@offworld> References: <20221215170909.2650271-1-fan.ni@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20221215170909.2650271-1-fan.ni@samsung.com> User-Agent: NeoMutt/20220429 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 Dec 2022, 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 Reviewed-by: Davidlohr Bueso