Re: [PATCH v5 33/40] x86/resctrl: Drop __init/__exit on assorted symbols

[James Morse]

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