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Tue, 29 Nov 2022 04:51:08 +0000 Message-ID: <4cee0097-4f08-1990-112f-6e39229f59ef@intel.com> Date: Tue, 29 Nov 2022 12:50:57 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.5.0 Subject: Re: [PATCH] nvme: clear the prp2 field of the nvme command. To: Chaitanya Kulkarni , "kbusch@kernel.org" , "axboe@fb.com" , "hch@lst.de" , "sagi@grimberg.me" , "linux-nvme@lists.infradead.org" , "linux-kernel@vger.kernel.org" References: <20221129014711.91305-1-lei.rao@intel.com> <15de4902-03e7-0d2c-4b4c-45d713d0f1fd@nvidia.com> Content-Language: en-US From: "Rao, Lei" In-Reply-To: <15de4902-03e7-0d2c-4b4c-45d713d0f1fd@nvidia.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI2PR04CA0008.apcprd04.prod.outlook.com (2603:1096:4:197::20) To DM8PR11MB5640.namprd11.prod.outlook.com (2603:10b6:8:3f::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM8PR11MB5640:EE_|DM8PR11MB5653:EE_ X-MS-Office365-Filtering-Correlation-Id: f99e7275-c70d-46b0-67b5-08dad1c553cc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM8PR11MB5640.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(136003)(346002)(376002)(366004)(396003)(39860400002)(451199015)(31686004)(83380400001)(6666004)(110136005)(6506007)(6486002)(36756003)(6512007)(31696002)(86362001)(38100700002)(26005)(82960400001)(186003)(2616005)(8936002)(5660300002)(8676002)(53546011)(478600001)(66476007)(41300700001)(66946007)(2906002)(66556008)(316002)(45980500001)(43740500002);DIR:OUT;SFP:1102; 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According to nvme spec, the prp2 is reserved if >> the data transfer does not cross a memory page boundary. Writing a >> reserved coded value into a controller property field produces undefined >> results, so it needs to be cleared in nvme_setup_rw(). >> >> Signed-off-by: Lei Rao > > if it is reserved then controller shoule ignore this field, no ? It's feasible for the controller to ignore this field. But our controller has stricter checks, and if prp2 is not used but has a value, some warnings will be printed. According to the NVMe spec, it seems to write a reserved field produces an undefined result, so maybe clearing it is better. Thanks, Lei > > not sure if original author wanted to avoid an extra assignment > in the fast path with assumption that reserved fields should be > ignored if it is then we should avoid this, if not then looks good > > Reviewed-by: Chaitanya Kulkarni > > -ck >