linux-kernel - Re: [RFC PATCH 27/36] arm_mpam: Allow configuration to be applied and restored during cpu online

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Message-ID: <4778e89f-0b94-441e-947a-dfc9839b250b@nvidia.com>
Date: Mon, 4 Aug 2025 09:39:14 -0700
From: Fenghua Yu <fenghuay@...dia.com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Cc: Rob Herring <robh@...nel.org>, Ben Horgan <ben.horgan@....com>,
 Rohit Mathew <rohit.mathew@....com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Zeng Heng
 <zengheng4@...wei.com>, Lecopzer Chen <lecopzerc@...dia.com>,
 Carl Worth <carl@...amperecomputing.com>,
 shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...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>, Koba Ko <kobak@...dia.com>
Subject: Re: [RFC PATCH 27/36] arm_mpam: Allow configuration to be applied and
 restored during cpu online

Hi, James,

On 7/11/25 11:36, James Morse wrote:
> When CPUs come online the original configuration should be restored.
> Once the maximum partid is known, allocate an configuration array for
> each component, and reprogram each RIS configuration from this.
>
> The MPAM spec describes how multiple controls can interact. To prevent
> this happening by accident, always reset controls that don't have a
> valid configuration. This allows the same helper to be used for
> configuration and reset.
>
> CC: Dave Martin <Dave.Martin@....com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
>   drivers/platform/arm64/mpam/mpam_devices.c  | 236 ++++++++++++++++++--
>   drivers/platform/arm64/mpam/mpam_internal.h |  26 ++-
>   2 files changed, 234 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/mpam_devices.c
> index bb3695eb84e9..f3ecfda265d2 100644
> --- a/drivers/platform/arm64/mpam/mpam_devices.c
> +++ b/drivers/platform/arm64/mpam/mpam_devices.c
> @@ -374,12 +374,16 @@ static void mpam_class_destroy(struct mpam_class *class)
>   	add_to_garbage(class);
>   }
>   
> +static void __destroy_component_cfg(struct mpam_component *comp);
> +
>   static void mpam_comp_destroy(struct mpam_component *comp)
>   {
>   	struct mpam_class *class = comp->class;
>   
>   	lockdep_assert_held(&mpam_list_lock);
>   
> +	__destroy_component_cfg(comp);
> +
>   	list_del_rcu(&comp->class_list);
>   	add_to_garbage(comp);
>   
> @@ -909,51 +913,90 @@ static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
>   		__mpam_write_reg(msc, reg, bm);
>   }
>   
> -static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
> +/* Called via IPI. Call while holding an SRCU reference */
> +static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
> +				      struct mpam_config *cfg)
>   {
>   	u16 bwa_fract = MPAMCFG_MBW_MAX_MAX;
>   	struct mpam_msc *msc = ris->vmsc->msc;
>   	struct mpam_props *rprops = &ris->props;
>   
> -	mpam_assert_srcu_read_lock_held();
> -
>   	mutex_lock(&msc->part_sel_lock);
>   	__mpam_part_sel(ris->ris_idx, partid, msc);
>   
> -	if (mpam_has_feature(mpam_feat_cpor_part, rprops))
> -		mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM, rprops->cpbm_wd);
> +	if (mpam_has_feature(mpam_feat_cpor_part, rprops)) {
> +		if (mpam_has_feature(mpam_feat_cpor_part, cfg))
> +			mpam_write_partsel_reg(msc, CPBM, cfg->cpbm);
> +		else
> +			mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM,
> +					      rprops->cpbm_wd);
> +	}
>   
> -	if (mpam_has_feature(mpam_feat_mbw_part, rprops))
> -		mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM, rprops->mbw_pbm_bits);
> +	if (mpam_has_feature(mpam_feat_mbw_part, rprops)) {
> +		if (mpam_has_feature(mpam_feat_mbw_part, cfg))
> +			mpam_write_partsel_reg(msc, MBW_PBM, cfg->mbw_pbm);
> +		else
> +			mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM,
> +					      rprops->mbw_pbm_bits);
> +	}
>   
>   	if (mpam_has_feature(mpam_feat_mbw_min, rprops))
>   		mpam_write_partsel_reg(msc, MBW_MIN, 0);
>   
> -	if (mpam_has_feature(mpam_feat_mbw_max, rprops))
> -		mpam_write_partsel_reg(msc, MBW_MAX, bwa_fract);
> +	if (mpam_has_feature(mpam_feat_mbw_max, rprops)) {
> +		if (mpam_has_feature(mpam_feat_mbw_max, cfg))
> +			mpam_write_partsel_reg(msc, MBW_MAX, cfg->mbw_max);
> +		else
> +			mpam_write_partsel_reg(msc, MBW_MAX, bwa_fract);
> +	}
>   
>   	if (mpam_has_feature(mpam_feat_mbw_prop, rprops))
>   		mpam_write_partsel_reg(msc, MBW_PROP, bwa_fract);
>   	mutex_unlock(&msc->part_sel_lock);
>   }
>   
> +struct reprogram_ris {
> +	struct mpam_msc_ris *ris;
> +	struct mpam_config *cfg;
> +};
> +
> +/* Call with MSC lock held */
> +static int mpam_reprogram_ris(void *_arg)
> +{
> +	u16 partid, partid_max;
> +	struct reprogram_ris *arg = _arg;
> +	struct mpam_msc_ris *ris = arg->ris;
> +	struct mpam_config *cfg = arg->cfg;
> +
> +	if (ris->in_reset_state)
> +		return 0;
> +
> +	spin_lock(&partid_max_lock);
> +	partid_max = mpam_partid_max;
partid_max is not used after the assignment.
> +	spin_unlock(&partid_max_lock);

Doesn't make sense to lock protect a local variable partid_max which is 
not used any way.

[SNIP]

Thanks.

-Fenghua