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Message-ID: <2bcd9829-498b-228a-2a86-67f8c6e859aa@suse.com> Date: Mon, 13 Mar 2023 17:55:09 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] xen/grants: repurpose command line max options Content-Language: en-US To: Roger Pau Monne Cc: Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu , xen-devel@lists.xenproject.org References: <20230313121632.86789-1-roger.pau@citrix.com> From: Jan Beulich In-Reply-To: <20230313121632.86789-1-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR2P281CA0091.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:9b::10) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|DUZPR04MB9795:EE_ X-MS-Office365-Filtering-Correlation-Id: 767a859d-1923-4f11-eaab-08db23e3b550 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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This value is an upper boundary of the per-domain > -value settable via Xen tools. > +Specify the default maximum number of frames which any domain may use as part > +of its grant table unless a different value is specified at domain creation. > > Dom0 is using this value for sizing its grant table. dom0less DomU-s do as well, at the very least, also ... > @@ -1245,9 +1244,10 @@ Dom0 is using this value for sizing its grant table. > > > Can be modified at runtime > > -Specify the maximum number of frames to use as part of a domains > -maptrack array. This value is an upper boundary of the per-domain > -value settable via Xen tools. > +Specify the default maximum number of frames to use as part of a domains > +maptrack array unless a different value is specified at domain creation. > + > +Dom0 is using this value for sizing its maptrack array. ... here. And even ordinary DomU-s appear to default to that in the absence of a specific value in the guest config. IOW at the very least the info you add should not be misleading. Better would be if the pre- existing info was adjusted at the same time. I also wonder about the specific wording down here: While the max grant table size can indeed be queried, this isn't the case for the maptrack array. A domain also doesn't need to know its size, so maybe "This value is used to size all domains' maptrack arrays, unless overridden by their guest config"? > --- a/xen/common/grant_table.c > +++ b/xen/common/grant_table.c > @@ -1956,18 +1956,15 @@ int grant_table_init(struct domain *d, int max_grant_frames, > return -EINVAL; > } > > - /* Default to maximum value if no value was specified */ > + /* Apply defaults if no value was specified */ > if ( max_grant_frames < 0 ) > max_grant_frames = opt_max_grant_frames; > if ( max_maptrack_frames < 0 ) > max_maptrack_frames = opt_max_maptrack_frames; > > - if ( max_grant_frames < INITIAL_NR_GRANT_FRAMES || > - max_grant_frames > opt_max_grant_frames || > - max_maptrack_frames > opt_max_maptrack_frames ) > + if ( max_grant_frames < INITIAL_NR_GRANT_FRAMES ) > { > - dprintk(XENLOG_INFO, "Bad grant table sizes: grant %u, maptrack %u\n", > - max_grant_frames, max_maptrack_frames); > + dprintk(XENLOG_INFO, "Bad grant table size %u\n", max_grant_frames); > return -EINVAL; > } I think I agree with the relaxation done here, but I also think this not introducing security concerns wants spelling out in the description: My understanding is that even in disaggregated environments we assume only fully privileged entities can create domains. Jan