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Message-ID: <58d5e890-e052-47df-42bb-6cc84aedd4a9@suse.com> Date: Tue, 8 Nov 2022 18:03:54 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.4.1 Subject: Re: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: Henry.Wang@arm.com, Andrew Cooper , George Dunlap , Wei Liu , =?UTF-8?B?RWR3aW4gVMO2csO2aw==?= , xen-devel@lists.xenproject.org References: <20221108113850.61619-1-roger.pau@citrix.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: AS9PR06CA0288.eurprd06.prod.outlook.com (2603:10a6:20b:45a::19) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|DU2PR04MB9210:EE_ X-MS-Office365-Filtering-Correlation-Id: 9fae40c1-eed0-41cb-2901-08dac1ab38ac X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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>>> - return 0; >>> + return -EINVAL; >>> } >> >> ... going from "success" to "failure" here has a meaningful risk of >> regressing callers. It is my understanding that it was deliberate to >> mimic success in this case (without meaning to assign "good" or "bad" >> to that decision). > > I would assume that was the original intention, yes, albeit the commit > message doesn't go into details about why mimicking success is > required, it's very well possible the code relying on this was xend. Quite possible, but you never know who else has cloned code from there. >> Can you instead fill the data to be returned in >> some simple enough way? I assume a mere memset() isn't going to be >> good enough, though (albeit public/domctl.h doesn't explicitly name >> any input-only fields, so it may not be necessary to preserve >> anything). Maybe zeroing ->mb and ->stats would do? > > Hm, it still feels kind of wrong. We do return errors elsewhere for > operations attempted against dying domains, and that seems all fine, > not sure why paging operations need to be different in this regard. > Arm does also return -EINVAL in that case. > > So what about postponing this change to 4.18 in order to avoid > surprises, but then taking it in its current form at the start of the > development window, as to have time to detect any issues? Maybe, but to be honest I'm not convinced. Arm can't really be taken for comparison, since the op is pretty new there iirc. >> As a minor remark: _If_ you're changing the printk(), then please >> also switch to using %pd. > > I've considered this, but then printing: "Tried to do a paging domctl > op on dying domain dX" felt kind of repetitive to me because of the > usage of domain and dX in the same sentence. Anyway, will adjust. Simply drop the word "domain", as we've done elsewhere when switching to %pd? Jan