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Fri, 21 Feb 2025 20:16:57 +0000 Message-ID: <0172ee7d-9a5c-44bf-8004-4d93c3d53cbe@intel.com> Date: Fri, 21 Feb 2025 12:16:54 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 23/23] x86/resctrl: Introduce interface to modify assignment states of the groups To: Dave Martin , "Moger, Babu" CC: "Moger, Babu" , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <1ccb907b-e8c9-4997-bc45-4a457ee84494@amd.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0234.namprd04.prod.outlook.com (2603:10b6:303:87::29) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|CH0PR11MB5252:EE_ X-MS-Office365-Filtering-Correlation-Id: cb0d99e0-5c3f-4342-b4c4-08dd52b4b0fa X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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>> int n; >> >> file = fopen("/sys/fs/resctrl/info/L3_MON/mbm_assign_control", "w"); >> >> if (file == NULL) { >> printf("Error opening file!\n"); >> return 1; >> } >> >> printf("File opened successfully.\n"); >> >> for (n = 0; n < 100; n++) >> if >> (fputs("test//0=tl;1=tl;2=tl;3=tl;4=tl;5=tl;9=tl;10=tl;11=tl\n", file) == EOF) >> fprintf(stderr, "Failed on interation %d error >> %s\n ", n, strerror(errno)); >> >> if (fclose(file) == 0) { >> printf("File closed successfully.\n"); >> } else { >> printf("Error closing file!\n"); >> } >> } > > Right. > >> When the buffer overflow happens the newline will not be there. I have >> added this error via rdt_last_cmd_puts. At least user knows there is an error. >> >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index 484d6009869f..70a96976e3ab 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> @@ -1250,8 +1252,10 @@ static ssize_t >> resctrl_mbm_assign_control_write(struct kernfs_open_file *of, >> int ret; >> >> /* Valid input requires a trailing newline */ >> - if (nbytes == 0 || buf[nbytes - 1] != '\n') >> + if (nbytes == 0 || buf[nbytes - 1] != '\n') { >> + rdt_last_cmd_puts("mbm_cntr_assign: buffer invalid\n"); >> return -EINVAL; >> + } >> >> buf[nbytes - 1] = '\0'; >> >> >> >> I am open to other ideas to handle this case. > > Reinette, what do you think about this as a stopgap approach? This seems fair. I expect that we need to document somewhere that writes "may" (to leave wiggle room for improvements) require page sized writes. > > The worst that happens is that userspace gets an unexpected failure in > scenarios that seem unlikely in the near future (i.e., where there are > a lot of RMIDs available, and at the same time groups have been given > stupidly long names). > > Since this is an implementation issue rather than an interface issue, > we could fix it later on. > > > Longer term, we may want to define some stuff along the lines of > > struct rdtgroup_file { > /* persistent data for an rdtgroup open file instance */ > }; > > static int rdtgroup_file_open(struct kernfs_open_file *of) > { > struct rdtgroup_file *rf; > > rf = kzalloc(sizeof(*rf), GFP_KERNEL); > if (!rf) > return -ENOMEM; > > of->priv; > } > > static void rdtgroup_file_release(struct kernfs_open_file *of) > { > /* > * Deal with dangling data and do cleanup appropriate > * for whatever kind of file this is, then: > */ > kfree(of->priv); > } > > > Then we'd have somewhere to stash data that needs to be carried over > from one read/write call to the next. Something like this seems needed for reading from this file. > > I tried to port my schemata buffering hack over, but the requirements > are not exactly the same as for mbm_assign_control, so it wasn't > trivial. It feels do-able, but it might be better to stabilise this > series before going down that road. > > (I'm happy to spend some time trying to wire this up if it would be > useful, though.) I was hoping that we would not need to re-invent something here. This does not seem like a new problem. Reinette