Received-SPF: pass (google.com: domain of linux-kernel+bounces-103487-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <fed6affb-c7f4-4992-8646-8f5a52c33966@intel.com>
Date: Thu, 14 Mar 2024 08:25:06 -0700
User-Agent: Mozilla Thunderbird
Subject: 32bit resctrl? (was Re: [PATCH v2] fs/resctrl: fix domid loss
 precision issue)
Content-Language: en-US
To: Rex Nie <rex.nie@jaguarmicro.com>, <james.morse@arm.com>, "x86@kernel.org"
	<x86@kernel.org>, "Luck, Tony" <tony.luck@intel.com>, Babu Moger
	<babu.moger@amd.com>, Peter Newman <peternewman@google.com>, Borislav Petkov
	<bp@alien8.de>
CC: <fenghua.yu@intel.com>, <ilpo.jarvinen@linux.intel.com>,
	<linux-kernel@vger.kernel.org>
References: <20240312075349.977-1-rex.nie@jaguarmicro.com>
From: Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <20240312075349.977-1-rex.nie@jaguarmicro.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?L1A1OVQrQ3JuaHpNN2FGdjZqR0pvSXk0T0g2cEhaSWNJcVVnaGtxcXgxMXZJ?=
 =?utf-8?B?OUF1WWRTQk9QS3RUbVJuREpPMHRIbW5GZnBHSnF2WHpVYkkyVlFFbi9UU2xD?=
 =?utf-8?B?M2VDdE1wWEJ4ZkY5VW11MEFmanora0tucitvNnFnZGRJZ01MTWtBMXZlVW1l?=
 =?utf-8?B?WlhQUTlhYmdQNUVXUks2RjUyeGh2OXl3VmUvMExubW1xSmd0cDZhd2FtdllR?=
 =?utf-8?B?dGxaUG0wa0pJMldQZnAzdUxZdE9saTlXREs5ZmpIbzFpb0JEbUVJZ3A0LzRw?=
 =?utf-8?B?UXRvanBUYmJVYUhHMDdtc1hMbHdCRXpKUStSY0Q3MGJ6dU9JZ3NIZWF5cXFZ?=
 =?utf-8?B?VVVKdWFwMEgzZ1hXdjQycXVwdEcxaWlNOVpEeEgvUmZHYksyOVpKRiszTzBN?=
 =?utf-8?B?b0FTVGYzcjVMTU5lN2Z4Q245cDFxSU1XUEJyaG1JWXV2WC9PbzB5dkZCTkQz?=
 =?utf-8?B?TjZQWDJqVmZCWUZGZHgvTWtnTUZHS3lybHZ2eG4zV0pyR1FCa000blhvamxj?=
 =?utf-8?B?MmFTL1l6WkpEOGFYVER6c202L2h4VHo4ZXQ3V3FseDQwUFVNNkdkTG91c2Np?=
 =?utf-8?B?WG9JdU5GMFNqREtnQmZISlZQUGFFU2w1M1FCTm1YNjNXaktKTXNya2dqSXNU?=
 =?utf-8?B?YUI3NzJ0WFdra3JIN3NlM2pmekxZcm5ha21KdFhoYmFVTE5ET2VaMWtlaG1v?=
 =?utf-8?B?aDFySkRZVnlvZ3hOMWl3WnBrS1J0SWFLOE1icHBaV0pXTWxULzA3MUFjV2d3?=
 =?utf-8?B?Y2FVK0t1SUZJYjloRHVsMWl1WUFzaGwzRkRkaTRTdnlMUTZmcWNNUEpOWjNR?=
 =?utf-8?B?NjYxUDFWRzhkRHkyK2xwSkdWY054RUc5VG5UcE5UZWpBZWl6azdLOTFEaUNH?=
 =?utf-8?B?d3diS1l6RzZPODVHRzYyMkhKbDI2Qlo2WG5LK1RWbE9aYlA3VjVMNTNuejFQ?=
 =?utf-8?B?ODBXV1VkeHBRVDNvM016M3RSc0RLTGZSSFFvSlJGTEJuTkhEOWp1cUpBM3c0?=
 =?utf-8?B?N0sxR3ExTi83MWk5ZDMrS2tjS2ZUVGxHelJTcTdBMzNwYmt2Nk1Dc1h1VzVB?=
 =?utf-8?B?VW1TR3FYbi81U3dMYVEwaE4raXZXVDhZais0T2pYbFJSUXZjYSsrcmdyL1NZ?=
 =?utf-8?B?Zzh0bmYxeEhzSXpybDBMWGhoTkIxV0kvTUsyQmdGTG1RcU5KZ2l5M3dkV0ow?=
 =?utf-8?B?Qm9wRTlwclNFa244K29PcGtsTWpIUFRMRE5TM2JWVEVBeVlNZkZyeEpBTkpL?=
 =?utf-8?B?T0xUYkR3UFFiZXBmamFkUU91SmhCUnVhOXZabWJLMVJDUk5SSlVBWXVrb25h?=
 =?utf-8?B?U3dKa2gwcnZoY3FjZjAwM0piZS9ldjFMZUF2dTdkYTFIVU05a1pSLzNVcW00?=
 =?utf-8?B?Zms2MW90TU9jdEZQdm51YkgrUFo0OFZFNTJsUjkzV0NBMnVUdFFXYnJYRk9z?=
 =?utf-8?B?L3Z5NEp3aStBUVhjeWNVcGNSLzY3bGpoMFExbDJGcmhvbExMNWZYZDU0c3d1?=
 =?utf-8?B?TUhONW9JZXVHamJkVGRKNTdFNTN1MzI2V1lSN0F6NUZCdDJQMFYzNGNuRGRa?=
 =?utf-8?B?ZkhmZDQ0SkVabTFubGVxUCtlSWRkTE15eG1IV0x2UzRDVVJVUS94T1VvUW5F?=
 =?utf-8?B?Y05RZVZjTVB2QVFMSHJPc0NmWTROU2M0R0FNamRtdFRGekZWMTNETmM2M3ZW?=
 =?utf-8?B?a29RTzZCZ2FUbGoxS3JRWXpOUmdEU3VjYUpodDdEMkJUYks1aUk0MFhsakNQ?=
 =?utf-8?B?aUhVcXcyOG9DWXZpTm95SXB0M3lnejVwcXc4QVJCZzhrZytPeHpHR3FoQTQv?=
 =?utf-8?B?U2tlci94K1VxL1QvVnRtYmZ4K0kyT3lpb0JkOG1VL3N6QkdIQWJSeDk5RWxJ?=
 =?utf-8?B?cTF3YWo5bGRjY2d3bS9leDZHRE56K01Yd1h5SmtBL2wzZHdwS1V5RndhdWZi?=
 =?utf-8?B?U2JiTkhLOHlxc2Jic25Qb0Q3SEQ1dkRXNjV2Vm1PZXBzblR1b0h3em1LRXFW?=
 =?utf-8?B?UUlUc3pndENSZWwzZWJBU2YvR29nTkJUYjdkUGdDcExpbXdzSlhQQmJNbFVZ?=
 =?utf-8?B?WW92WDRIeSttQTdKa1FJRmZ6cnh1eUprTW4vTWF3VlBxamtWK1YwR2JJL21R?=
 =?utf-8?B?OW5LL1FNTFlKTUJEOGlGRWl3M0FBeGNCTmZtS2ZBMCs2Yy9WMmp2ZkdDYTYz?=
 =?utf-8?B?cEE9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: b67e2f77-58c0-43c0-d1e0-08dc443aeec7
X-MS-Exchange-CrossTenant-AuthSource: SJ2PR11MB7573.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Mar 2024 15:25:08.6637
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: f/LIzUhy1xHJt4LM05WzSRQqH/c/V9wgGjnStXGdwY4/R3erIqu2ADdnmcwj0vu7xjSWbtqLZnQZMe8PBNgSdprveyDhKwMXb0zCzkCvx9Y=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR11MB8176
X-OriginatorOrg: intel.com

+x86 maintainers, Tony, Babu, Peter

Hi Everybody,

On 3/12/2024 12:53 AM, Rex Nie wrote:
> Below statement from mkdir_mondata_subdir function will loss precision,
> because it assigns int to 14 bits bitfield.
> 	priv.u.domid = d->id;
> 
> On some platforms(e.g.,x86), the max cache_id is the amount of L3 caches,
> so it is not in the range of 0x3fff. But some platforms use higher
> cache_id, e.g., arm uses cache_id as locator for cache MSC. This will
> cause below issue if cache_id > 0x3fff likes:
> /sys/fs/resctrl/mon_groups/p1/mon_data/mon_L3_1048564 # cat llc_occupancy
> cat: read error: No such file or directory
> 
> This is the call trace when cat llc_occupancy:
> rdtgroup_mondata_show()
> 	domid = md.u.domid
> 	d = resctrl_arch_find_domain(r, domid)
> 
> d is null here because of lossing precision
> 
> Signed-off-by: Rex Nie <rex.nie@jaguarmicro.com>
> ---
>  fs/resctrl/internal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 7a6f46b4edd0..096317610949 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -94,7 +94,7 @@ union mon_data_bits {
>  	struct {
>  		unsigned int rid		: 10;
>  		enum resctrl_event_id evtid	: 8;
> -		unsigned int domid		: 14;
> +		u32				domid;
>  	} u;
>  };
>  

resctrl currently supports 32bit builds. Fixing this issue* in this way
would first require that resctrl (the architecture independent fs part)
depend on X86_64. Is this a change that everybody will be comfortable with?

(Of course, there are other solutions available to address the issue mentioned
in this patch that do not require depending on X86_64, but I would like
to take this moment to understand the sentiment surrounding continuing support
for 32bit resctrl.)

Thank you.

Reinette

* Please note that this is not an urgent fix but instead a preparatory change
  for future Arm support.