linux-kernel - Re: [RFC PATCH 09/19] x86/resctrl: Add plza_capable in rdt

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Message-ID: <ed2d089b-0249-4f1a-8da2-5e61d5d1158f@intel.com>
Date: Wed, 11 Feb 2026 08:54:21 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ben Horgan <ben.horgan@....com>, Babu Moger <babu.moger@....com>,
	<corbet@....net>, <tony.luck@...el.com>, <Dave.Martin@....com>,
	<james.morse@....com>, <tglx@...nel.org>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <peterz@...radead.org>,
	<juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
	<dietmar.eggemann@....com>, <rostedt@...dmis.org>, <bsegall@...gle.com>,
	<mgorman@...e.de>, <vschneid@...hat.com>, <akpm@...ux-foundation.org>,
	<pawan.kumar.gupta@...ux.intel.com>, <pmladek@...e.com>,
	<feng.tang@...ux.alibaba.com>, <kees@...nel.org>, <arnd@...db.de>,
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	<kvm@...r.kernel.org>, <peternewman@...gle.com>, <eranian@...gle.com>,
	<gautham.shenoy@....com>
Subject: Re: [RFC PATCH 09/19] x86/resctrl: Add plza_capable in rdt_resource
 data structure

Hi Ben,

On 2/11/26 7:19 AM, Ben Horgan wrote:
> Hi Babu,
> 
> On 1/21/26 21:12, Babu Moger wrote:
>> Add plza_capable field to the rdt_resource structure to indicate whether
>> Privilege Level Zero Association (PLZA) is supported for that resource
>> type.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>>  arch/x86/kernel/cpu/resctrl/core.c     | 6 ++++++
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 5 +++++
>>  include/linux/resctrl.h                | 3 +++
>>  3 files changed, 14 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>> index 2de3140dd6d1..e41fe5fa3f30 100644
>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>> @@ -295,6 +295,9 @@ static __init bool __rdt_get_mem_config_amd(struct rdt_resource *r)
>>  
>>  	r->alloc_capable = true;
>>  
>> +	if (rdt_cpu_has(X86_FEATURE_PLZA))
>> +		r->plza_capable = true;
>> +
>>  	return true;
>>  }
>>  
>> @@ -314,6 +317,9 @@ static void rdt_get_cache_alloc_cfg(int idx, struct rdt_resource *r)
>>  	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
>>  		r->cache.arch_has_sparse_bitmasks = ecx.split.noncont;
>>  	r->alloc_capable = true;
>> +
>> +	if (rdt_cpu_has(X86_FEATURE_PLZA))
>> +		r->plza_capable = true;
>>  }
>>  
>>  static void rdt_get_cdp_config(int level)
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 885026468440..540e1e719d7f 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -229,6 +229,11 @@ bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level l)
>>  	return rdt_resources_all[l].cdp_enabled;
>>  }
>>  
>> +bool resctrl_arch_get_plza_capable(enum resctrl_res_level l)
>> +{
>> +	return rdt_resources_all[l].r_resctrl.plza_capable;
>> +}
>> +
>>  void resctrl_arch_reset_all_ctrls(struct rdt_resource *r)
>>  {
>>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index 63d74c0dbb8f..ae252a0e6d92 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -319,6 +319,7 @@ struct resctrl_mon {
>>   * @name:		Name to use in "schemata" file.
>>   * @schema_fmt:		Which format string and parser is used for this schema.
>>   * @cdp_capable:	Is the CDP feature available on this resource
>> + * @plza_capable:	Is Privilege Level Zero Association capable?
>>   */
>>  struct rdt_resource {
>>  	int			rid;
>> @@ -334,6 +335,7 @@ struct rdt_resource {
>>  	char			*name;
>>  	enum resctrl_schema_fmt	schema_fmt;
>>  	bool			cdp_capable;
>> +	bool			plza_capable;
> 
> Why are you making plza a resource property? Certainly for MPAM we'd
> want this to be global across resources and I see above that you are
> just checking a cpu property rather then anything per resource.

I agree. For reference: https://lore.kernel.org/lkml/6fe647ce-2e65-45dd-9c79-d1c2cb0991fe@intel.com/

One possible concern for MPAM related to this caught my eye. From
https://lore.kernel.org/lkml/20260203214342.584712-10-ben.horgan@arm.com/ :

	If an SMCU is not shared with other cpus then it is implementation
	defined whether the configuration from MPAMSM_EL1 is used or that from
	the appropriate MPAMy_ELx. As we set the same, PMG_D and PARTID_D,
	configuration for MPAM0_EL1, MPAM1_EL1 and MPAMSM_EL1 the resulting
	configuration is the same regardless.

I admit that I am not yet comfortable with the MPAM register usages ... but from
above it sounds to me as though if resctrl associates different CLOSID/PARTID and
RMID/PMG with a task to be used at different privilege levels as planned with this
work then the mapping to MPAM0_EL1 and MPAM1_EL1 may be easy but MPAMSM_EL1 may be
difficult?  


Reinette