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Message-ID: Date: Tue, 8 Nov 2022 17:14:40 +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: Roger Pau Monne 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: <20221108113850.61619-1-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR0P281CA0100.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:a9::6) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AM9PR04MB8858:EE_ X-MS-Office365-Filtering-Correlation-Id: 56fbfc0d-d8b2-4147-ef2d-08dac1a457c3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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While I can see how the present behavior is problematic when it comes to consuming supposedly returned data, ... > --- a/xen/arch/x86/mm/paging.c > +++ b/xen/arch/x86/mm/paging.c > @@ -694,9 +694,10 @@ int paging_domctl(struct domain *d, struct xen_domctl_shadow_op *sc, > > if ( unlikely(d->is_dying) ) > { > - gdprintk(XENLOG_INFO, "Ignoring paging op on dying domain %u\n", > + gdprintk(XENLOG_INFO, > + "Tried to do a paging domctl op on dying domain %u\n", > d->domain_id); > - 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). 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? As a minor remark: _If_ you're changing the printk(), then please also switch to using %pd. Jan