linux-kernel - Re: [PATCH v13 10/27] x86/resctrl: Add data structures and definitions for ABMC assignment

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Message-ID: <63e37e50-10f6-4408-a89d-a5f4e8cd749c@intel.com>
Date: Thu, 22 May 2025 14:10:12 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <james.morse@....com>, <dave.martin@....com>, <fenghuay@...dia.com>,
	<x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<akpm@...ux-foundation.org>, <thuth@...hat.com>, <rostedt@...dmis.org>,
	<ardb@...nel.org>, <gregkh@...uxfoundation.org>,
	<daniel.sneddon@...ux.intel.com>, <jpoimboe@...nel.org>,
	<alexandre.chartre@...cle.com>, <pawan.kumar.gupta@...ux.intel.com>,
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	<maciej.wieczor-retman@...el.com>, <eranian@...gle.com>,
	<Xiaojian.Du@....com>, <gautham.shenoy@....com>
Subject: Re: [PATCH v13 10/27] x86/resctrl: Add data structures and
 definitions for ABMC assignment

Hi Babu,

On 5/15/25 3:51 PM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign a hardware
> counter to an RMID, event pair and monitor the bandwidth as long as the
> counter is assigned. The bandwidth events will be tracked by the hardware
> until the user changes the configuration. Each resctrl group can configure
> maximum two counters, one for total event and one for local event.

(please update, above describes previous design)

> 
> The ABMC feature implements an MSR L3_QOS_ABMC_CFG (C000_03FDh).
> ABMC counter assignment is done by setting the counter id, bandwidth
> source (RMID) and bandwidth configuration. Users will have the option to
> change the bandwidth configuration using resctrl interface which will be
> introduced later in the series.

"will be introduced later in the series" is similar to "in a subsequent patch"
and should not be used in a changelog. Just describe what this patch does.

> 
> Attempts to read or write the MSR when ABMC is not enabled will result
> in a #GP(0) exception.
> 
> Introduce the data structures and definitions for MSR L3_QOS_ABMC_CFG
> (0xC000_03FDh):
> =========================================================================
> Bits 	Mnemonic	Description			Access Reset
> 							Type   Value
> =========================================================================
> 63 	CfgEn 		Configuration Enable 		R/W 	0
> 
> 62 	CtrEn 		Enable/disable counting		R/W 	0
> 
> 61:53 	– 		Reserved 			MBZ 	0
> 
> 52:48 	CtrID 		Counter Identifier		R/W	0
> 
> 47 	IsCOS		BwSrc field is a CLOSID		R/W	0
> 			(not an RMID)
> 
> 46:44 	–		Reserved			MBZ	0
> 
> 43:32	BwSrc		Bandwidth Source		R/W	0
> 			(RMID or CLOSID)
> 
> 31:0	BwType		Bandwidth configuration		R/W	0
> 			to track for this counter
> ==========================================================================
> 
> The feature details are documented in the APM listed below [1].
> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth
> Monitoring (ABMC).
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
> v13: Removed the Reviewed-by tag as there is commit log change to remove
>      BMEC reference.
> 
> v12: No changes.
> 
> v11: No changes.
> 
> v10: No changes.
> 
> v9: Removed the references of L3_QOS_ABMC_DSC.
>     Text changes about configuration in kernel doc.
> 
> v8: Update the configuration notes in kernel_doc.
>     Few commit message update.
> 
> v7: Removed the reference of L3_QOS_ABMC_DSC as it is not used anymore.
>     Moved the configuration notes to kernel_doc.
>     Adjusted the tabs for l3_qos_abmc_cfg and checkpatch seems happy.
> 
> v6: Removed all the fs related changes.
>     Added note on CfgEn,CtrEn.
>     Removed the definitions which are not used.
>     Removed cntr_id initialization.
> 
> v5: Moved assignment flags here (path 10/19 of v4).
>     Added MON_CNTR_UNSET definition to initialize cntr_id's.
>     More details in commit log.
>     Renamed few fields in l3_qos_abmc_cfg for readability.
> 
> v4: Added more descriptions.
>     Changed the name abmc_ctr_id to ctr_id.
>     Added L3_QOS_ABMC_DSC. Used for reading the configuration.
> 
> v3: No changes.
> 
> v2: No changes.
> ---
>  arch/x86/include/asm/msr-index.h       |  1 +
>  arch/x86/kernel/cpu/resctrl/internal.h | 35 ++++++++++++++++++++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 3970e0b16e47..b5b5ebead24f 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1203,6 +1203,7 @@
>  /* - AMD: */
>  #define MSR_IA32_MBA_BW_BASE		0xc0000200
>  #define MSR_IA32_SMBA_BW_BASE		0xc0000280
> +#define MSR_IA32_L3_QOS_ABMC_CFG	0xc00003fd
>  #define MSR_IA32_L3_QOS_EXT_CFG		0xc00003ff
>  #define MSR_IA32_EVT_CFG_BASE		0xc0000400
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index fcc9d23686a1..db6b0c28ee6b 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -164,6 +164,41 @@ union cpuid_0x10_x_edx {
>  	unsigned int full;
>  };
>  
> +/*
> + * ABMC counters are configured by writing to L3_QOS_ABMC_CFG.
> + * @bw_type		: Bandwidth configuration (supported by BMEC)
> + *			  tracked by the @cntr_id.

The "supported by BMEC" is unexpected with the new design that separated
the two features.

> + * @bw_src		: Bandwidth source (RMID or CLOSID).
> + * @reserved1		: Reserved.
> + * @is_clos		: @bw_src field is a CLOSID (not an RMID).
> + * @cntr_id		: Counter identifier.
> + * @reserved		: Reserved.
> + * @cntr_en		: Counting enable bit.
> + * @cfg_en		: Configuration enable bit.
> + *
> + * Configuration and counting:
> + * Counter can be configured across multiple writes to MSR. Configuration
> + * is applied only when @cfg_en = 1. Counter @cntr_id is reset when the
> + * configuration is applied.
> + * @cfg_en = 1, @cntr_en = 0 : Apply @cntr_id configuration but do not
> + *                             count events.
> + * @cfg_en = 1, @cntr_en = 1 : Apply @cntr_id configuration and start
> + *                             counting events.
> + */
> +union l3_qos_abmc_cfg {
> +	struct {
> +		unsigned long bw_type  :32,
> +			      bw_src   :12,
> +			      reserved1: 3,
> +			      is_clos  : 1,
> +			      cntr_id  : 5,
> +			      reserved : 9,
> +			      cntr_en  : 1,
> +			      cfg_en   : 1;
> +	} split;
> +	unsigned long full;
> +};
> +
>  void rdt_ctrl_update(void *arg);
>  
>  int rdt_get_mon_l3_config(struct rdt_resource *r);

Reinette