linux-kernel - Re: [PATCH v6 29/42] x86/resctrl: Move get_config

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ce60836d-d482-45c7-842b-d7e28e9bf794@intel.com>
Date: Fri, 28 Feb 2025 18:28:12 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>, Babu Moger
	<Babu.Moger@....com>, <shameerali.kolothum.thodi@...wei.com>, "D Scott
 Phillips OS" <scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
	"Dave Martin" <dave.martin@....com>, Koba Ko <kobak@...dia.com>, Shanker
 Donthineni <sdonthineni@...dia.com>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>, "Tony Luck" <tony.luck@...el.com>
Subject: Re: [PATCH v6 29/42] x86/resctrl: Move get_config_index() to a header

Hi James,

On 2/28/25 11:51 AM, James Morse wrote:
> Hi Reinette,
> 
> On 20/02/2025 01:27, Reinette Chatre wrote:
>> On 2/7/25 10:18 AM, James Morse wrote:
>>> get_config_index() is used by the architecture specific code to map a
>>> CLOSID+type pair to an index in the configuration arrays.
>>>
>>> MPAM needs to do this too to preserve the ABI to user-space, there is
>>> no reason to do it differently.
>>>
>>> Move the helper to a header file.
> 
>>> --- a/include/linux/resctrl.h
>>> +++ b/include/linux/resctrl.h
>>> @@ -384,6 +384,21 @@ void resctrl_arch_mon_event_config_write(void *config_info);
>>>   */
>>>  void resctrl_arch_mon_event_config_read(void *config_info);
>>>  
>>> +/* For use by arch code to remap resctrl's smaller CDP CLOSID range */
>>> +static inline u32 resctrl_get_config_index(u32 closid,
>>> +					   enum resctrl_conf_type type)
>>> +{
>>> +	switch (type) {
>>> +	default:
>>> +	case CDP_NONE:
>>> +		return closid;
>>> +	case CDP_CODE:
>>> +		return closid * 2 + 1;
>>> +	case CDP_DATA:
>>> +		return closid * 2;
>>> +	}
>>> +}
>>> +
> 
>> Could you please add the motivation for the use of an inline function?
> 
> Putting this in the header file means it isn't duplicated, so its behaviour can't become

I am not following this. How would making this part of a .c file of fs/resctrl with just
the prototype in include/linux/resctrl.h result in this function being duplicated?

> different. If its in a header file, it has to be marked inline otherwise every C file that
> includes it gets a copy that probably isn't used, and upsets the linker.
> 
> Calling from the arch code into the filesystem prevents the arch code from being
> standalone. This is a useful direction of travel because it allows fs/resctrl to one
> day become a module

Don't we have this already with all the needed CPU and domain management (
resctrl_online_ctrl_domain(), resctrl_online_mon_domain(), resctrl_online_cpu(),
resctrl_offline_cpu(), etc.)?

> 
> Today, the compiler is choosing to inline this:
> | x86_64-linux-objdump -d ctrlmondata.o | grep resctrl_get_config_index | wc -l
> | 0
> 
> This kind of arithmetic for an array lookup is the kind of thing its good to give the
> compiler full visibility of as its good fodder for constant folding.
> 
> For so few call sites, I don't think this is really worth thinking about.
> Forcing this call out of line makes the kernel text bigger, but only by 32 bytes.
> 
> 
> I've expanded the last paragraph of the commit message to read:
> | Move the helper to a header file to allow all architectures that either
> | use or emulate CDP to use the same pattern of CLOSID values. Moving
> | this to a header file means it must be marked inline, which matches
> | the existing compiler choice for this static function.
> 
> 

Reinette