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Tue, 4 May 2021 00:17:49 +0000 Received: from [10.2.50.162] (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 4 May 2021 00:17:48 +0000 Subject: Re: [PATCH 12/16] nvme-pci: Check DMA ops when indicating support for PCI P2PDMA To: Logan Gunthorpe , , , , , , CC: Stephen Bates , Christoph Hellwig , Dan Williams , Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy References: <20210408170123.8788-1-logang@deltatee.com> <20210408170123.8788-13-logang@deltatee.com> From: John Hubbard Message-ID: Date: Mon, 3 May 2021 17:17:48 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.145.6] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: d5974555-58c3-4bc7-9f0b-08d90e920cf2 X-MS-TrafficTypeDiagnostic: MN2PR12MB4485: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:6790; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 May 2021 00:17:49.2598 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d5974555-58c3-4bc7-9f0b-08d90e920cf2 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT005.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4485 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 35FCDC0007C9 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=OlZTKYPn; dmarc=pass (policy=none) header.from=nvidia.com; spf=none (imf06.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.236.71) smtp.mailfrom=jhubbard@nvidia.com X-Stat-Signature: bzssfhcqnd11dmjawu3uj49yqjrpgm8t Received-SPF: none (nvidia.com>: No applicable sender policy available) receiver=imf06; identity=mailfrom; envelope-from=""; helo=NAM11-BN8-obe.outbound.protection.outlook.com; client-ip=40.107.236.71 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620087473-107001 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 5/3/21 10:17 AM, Logan Gunthorpe wrote: ... >>> blk_queue_flag_set(QUEUE_FLAG_NONROT, ns->queue); >>> - if (ctrl->ops->flags & NVME_F_PCI_P2PDMA) >>> + if (ctrl->ops->supports_pci_p2pdma && >>> + ctrl->ops->supports_pci_p2pdma(ctrl)) >> >> This is a little excessive, as I suspected. How about providing a >> default .supports_pci_p2pdma routine that returns false, so that >> the op is always available (non-null)? By "default", maybe that >> means either requiring an init_the_ops_struct() routine to be >> used, and/or checking all the users of struct nvme_ctrl_ops. > > Honestly that sounds much more messy to me than simply checking if it's > NULL before using it (which is a common, accepted pattern for ops). OK, it's a minor suggestion, so feel free to ignore if you prefer it the other way, sure. > >> Another idea: maybe you don't really need a bool .supports_pci_p2pdma() >> routine at all, because the existing .flags really is about right. >> You just need the flags to be filled in dynamically. So, do that >> during nvme_pci setup/init time: that's when this module would call >> dma_pci_p2pdma_supported(). > > If the flag is filled in dynamically, then the ops struct would have to > be non-constant. Ops structs should be constant for security reasons. > Hadn't thought about keeping ops structs constant. OK. thanks, -- John Hubbard NVIDIA