Re: [RESEND PATCH v4 03/15] x86/resctrl: Add data structures and definitions for PLZA configuration

Hi Babu,

On 7/7/26 2:50 PM, Babu Moger wrote:
> Privilege Level Zero Association (PLZA) allows the kernel to use a
> different CLOSID (and optionally RMID) than user mode on entry to kernel
> mode. The CLOSID/RMID association is programmed per CPU via

CLOSID is also optional, no? I am not able to recall now why this is not made
optional in this implementation though. Could you please remind me and add
it to the changelog for next time?

> MSR_IA32_PQR_PLZA_ASSOC (0xc00003fc), using RMID/CLOSID values and their
> respective enable bits.
> 
> Add the MSR definition and union msr_pqr_plza_assoc to represent the MSR
> bitfield layout used by subsequent PLZA programming.
> 
> Signed-off-by: Babu Moger <[email protected]>
> ---
> v4: Re-wrote the changelog and code comment.
> 
> v3: No code changes. Patch order changed. Improved changelog.
> 
> v2: No changes. Just rebasing on top of the latest tip branch.
> ---
>  arch/x86/include/asm/msr-index.h       |  1 +
>  arch/x86/kernel/cpu/resctrl/internal.h | 37 ++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 18c4be75e927..2503451a95fe 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1292,6 +1292,7 @@
>  /* - AMD: */
>  #define MSR_IA32_MBA_BW_BASE		0xc0000200
>  #define MSR_IA32_SMBA_BW_BASE		0xc0000280
> +#define MSR_IA32_PQR_PLZA_ASSOC		0xc00003fc
>  #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 e3cfa0c10e92..020ebc2c8a1f 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -222,6 +222,43 @@ union l3_qos_abmc_cfg {
>  	unsigned long full;
>  };
>  
> +/*
> + * Privilege Level Zero Association (PLZA) is configured by writing to
> + * MSR_IA32_PQR_PLZA_ASSOC. The MSR must be programmed on every CPU in
> + * the QoS domain. Each domain supports only one PLZA CLOSID and/or RMID
> + * association. All fields other than PLZA_EN must hold the same value
> + * across the domain for consistent operation.
> + *
> + * When PLZA_EN is set, the CLOSID/RMID association used at CPL 0 is
> + * taken from MSR_IA32_PQR_PLZA_ASSOC instead of MSR_IA32_PQR_ASSOC.
> + *
> + * @rmid		: RMID associated with PLZA.
> + * @reserved1		: Reserved.
> + * @rmid_en		: Enable RMID association for PLZA.
> + * @closid		: CLOSID associated with PLZA.
> + * @reserved2		: Reserved.
> + * @closid_en		: Enable CLOSID association for PLZA.
> + * @reserved3		: Reserved.
> + * @plza_en		: Enable PLZA. When enabled, PLZA applies to the
> + *			  given CPU. When PLZA is disabled for a CPU, the
> + *			  CLOSID and RMID association defined in the
> + *			  PQR_ASSOC MSR applies, regardless of the CPU's

To support grep: "the PQR_ASSOC MSR" -> "MSR_IA32_PQR_ASSOC"

> + *			  privilege level.

Could this also please highlight the relationship between plza_en, rmid_en,
and closid_en? For example, if I understand correctly, when "rmid_en" is 0
then RMID is taken from MSR_IA32_PQR_ASSOC, similarly, when "closid_en" is 0
then CLOSID is taken from MSR_IA32_PQR_ASSOC. Thus, plza_en could be 1, but
if both "rmid_en" and "closid_en" are 0 then, the same behavior results as
described for plza_en == 0: "CLOSID and RMID association defined
in MSR_IA32_PQR_ASSOC applies, regardless of the CPU's privilege level".

> + */
> +union msr_pqr_plza_assoc {
> +	struct {
> +		unsigned long rmid	:12,
> +			      reserved1	:19,
> +			      rmid_en	: 1,
> +			      closid	: 4,
> +			      reserved2	:11,
> +			      closid_en	: 1,
> +			      reserved3	:15,
> +			      plza_en	: 1;
> +	} split;
> +	unsigned long full;
> +};
> +
>  void rdt_ctrl_update(void *arg);
>  
>  int rdt_get_l3_mon_config(struct rdt_resource *r);

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