linux-kernel - Re: [PATCH v5 33/40] x86/resctrl: Drop __init/_

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Message-ID: <72934529-d6a3-4231-8ed7-6e7dc4325e9c@arm.com>
Date: Fri, 7 Feb 2025 15:54:42 +0000
From: James Morse <james.morse@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>, 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>, Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v5 33/40] x86/resctrl: Drop __init/__exit on assorted
 symbols

Hi Reinette,

On 24/10/2024 00:56, Reinette Chatre wrote:
> On 10/4/24 11:03 AM, James Morse wrote:
>> Because ARM's MPAM controls are probed using MMIO, resctrl can't be
>> initialised until enough CPUs are online to have determined the
>> system-wide supported num_closid. Arm64 also supports 'late onlined
>> secondaries', where only a subset of CPUs are online during boot.
>>
>> These two combine to mean the MPAM driver may not be able to initialise
>> resctrl until user-space has brought 'enough' CPUs online.
>>
>> To allow MPAM to initialise resctrl after __init text has been free'd,
>> remove all the __init markings from resctrl.
>>
>> The existing __exit markings cause these functions to be removed by the
>> linker as it has never been possible to build resctrl as a module. MPAM
>> has an error interrupt which causes the driver to reset and disable
>> itself. Remove the __exit markings to allow the MPAM driver to tear down
>> resctrl when an error occurs.

>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>> index f484726a2588..f713ac628444 100644
>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>> @@ -775,7 +775,7 @@ struct rdt_options {
>>  	bool	force_off, force_on;
>>  };
>>  
>> -static struct rdt_options rdt_options[]  __initdata = {
>> +static struct rdt_options rdt_options[]  __ro_after_init = {
>>  	RDT_OPT(RDT_FLAG_CMT,	    "cmt",	X86_FEATURE_CQM_OCCUP_LLC),
>>  	RDT_OPT(RDT_FLAG_MBM_TOTAL, "mbmtotal", X86_FEATURE_CQM_MBM_TOTAL),
>>  	RDT_OPT(RDT_FLAG_MBM_LOCAL, "mbmlocal", X86_FEATURE_CQM_MBM_LOCAL),
>> @@ -815,7 +815,7 @@ static int __init set_rdt_options(char *str)
>>  }
>>  __setup("rdt", set_rdt_options);
>>  
>> -bool __init rdt_cpu_has(int flag)
>> +bool rdt_cpu_has(int flag)

> I assume this can be dropped when resctrl_arch_is_evt_configurable() uses
> a helper instead?

resctrl_arch_is_evt_configurable() is that helper! If we wanted to decouple this in the
x86 arch code, it could do the rdt_cpu_has() stuff at boot, then test flags in
rdt_mon_features - but that isn't how it works today, and I don't think its worth the churn.

This __init marker causes a mismatched-sections warning because its called via
resctrl_arch_is_evt_configurable() from non __init marked code.


Thanks,

James