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

[Ben Horgan <ben.horgan@arm.com>]

Hi James,

On 7/11/25 19:36, 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@arm.com>
> Signed-off-by: James Morse <james.morse@arm.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;
> +	spin_unlock(&partid_max_lock);
> +	for (partid = 0; partid <= partid_max; partid++)
> +		mpam_reprogram_ris_partid(ris, partid, cfg);
> +
> +	return 0;
> +}
> +
>   /*
>    * Called via smp_call_on_cpu() to prevent migration, while still being
>    * pre-emptible.
>    */
>   static int mpam_reset_ris(void *arg)
>   {
> -	u16 partid, partid_max;
>   	struct mpam_msc_ris *ris = arg;
> +	struct reprogram_ris reprogram_arg;
> +	struct mpam_config empty_cfg = { 0 };
>   
>   	if (ris->in_reset_state)
>   		return 0;
>   
> -	spin_lock(&partid_max_lock);
> -	partid_max = mpam_partid_max;
> -	spin_unlock(&partid_max_lock);
> -	for (partid = 0; partid < partid_max; partid++)
> -		mpam_reset_ris_partid(ris, partid);
> +	reprogram_arg.ris = ris;
> +	reprogram_arg.cfg = &empty_cfg;
> +
> +	mpam_reprogram_ris(&reprogram_arg);
>   
>   	return 0;
>   }
> @@ -984,13 +1027,11 @@ static int mpam_touch_msc(struct mpam_msc *msc, int (*fn)(void *a), void *arg)
>   
>   static void mpam_reset_msc(struct mpam_msc *msc, bool online)
>   {
> -	int idx;
>   	struct mpam_msc_ris *ris;
>   
>   	mpam_assert_srcu_read_lock_held();
>   
>   	mpam_mon_sel_outer_lock(msc);
> -	idx = srcu_read_lock(&mpam_srcu);
>   	list_for_each_entry_srcu(ris, &msc->ris, msc_list, srcu_read_lock_held(&mpam_srcu)) {
>   		mpam_touch_msc(msc, &mpam_reset_ris, ris);
>   
> @@ -1000,10 +1041,38 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
>   		 */
>   		ris->in_reset_state = online;
>   	}
> -	srcu_read_unlock(&mpam_srcu, idx);
>   	mpam_mon_sel_outer_unlock(msc);
>   }
>   
> +static void mpam_reprogram_msc(struct mpam_msc *msc)
> +{
> +	int idx;
> +	u16 partid;
> +	bool reset;
> +	struct mpam_config *cfg;
> +	struct mpam_msc_ris *ris;
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_rcu(ris, &msc->ris, msc_list) {
> +		if (!mpam_is_enabled() && !ris->in_reset_state) {
> +			mpam_touch_msc(msc, &mpam_reset_ris, ris);
> +			ris->in_reset_state = true;
> +			continue;
> +		}
> +
> +		reset = true;
> +		for (partid = 0; partid <= mpam_partid_max; partid++) {
Do we need to consider 'partid_max_lock' here?
> +			cfg = &ris->vmsc->comp->cfg[partid];
> +			if (cfg->features)
> +				reset = false;
> +
> +			mpam_reprogram_ris_partid(ris, partid, cfg);
> +		}
> +		ris->in_reset_state = reset;
> +	}
> +	srcu_read_unlock(&mpam_srcu, idx);
> +}
> +
>   static void _enable_percpu_irq(void *_irq)
>   {
>   	int *irq = _irq;
> @@ -1025,7 +1094,7 @@ static int mpam_cpu_online(unsigned int cpu)
>   			_enable_percpu_irq(&msc->reenable_error_ppi);
>   
>   		if (atomic_fetch_inc(&msc->online_refs) == 0)
> -			mpam_reset_msc(msc, true);
> +			mpam_reprogram_msc(msc);
>   	}
>   	srcu_read_unlock(&mpam_srcu, idx);
>   
> @@ -1806,6 +1875,43 @@ static void mpam_unregister_irqs(void)
>   	cpus_read_unlock();
>   }
>   
> +static void __destroy_component_cfg(struct mpam_component *comp)
> +{
> +	add_to_garbage(comp->cfg);
> +}
> +
> +static int __allocate_component_cfg(struct mpam_component *comp)
> +{
> +	if (comp->cfg)
> +		return 0;
> +
> +	comp->cfg = kcalloc(mpam_partid_max + 1, sizeof(*comp->cfg), GFP_KERNEL);
And here?
> +	if (!comp->cfg)
> +		return -ENOMEM;
> +	init_garbage(comp->cfg);
> +
> +	return 0;
> +}
> +
> +static int mpam_allocate_config(void)
> +{
> +	int err = 0;
> +	struct mpam_class *class;
> +	struct mpam_component *comp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_for_each_entry(class, &mpam_classes, classes_list) {
> +		list_for_each_entry(comp, &class->components, class_list) {
> +			err = __allocate_component_cfg(comp);
> +			if (err)
> +				return err;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>   static void mpam_enable_once(void)
>   {
>   	int err;
> @@ -1817,12 +1923,21 @@ static void mpam_enable_once(void)
>   	 */
>   	cpus_read_lock();
>   	mutex_lock(&mpam_list_lock);
> -	mpam_enable_merge_features(&mpam_classes);
> +	do {
> +		mpam_enable_merge_features(&mpam_classes);
>   
> -	err = mpam_register_irqs();
> -	if (err)
> -		pr_warn("Failed to register irqs: %d\n", err);
> +		err = mpam_allocate_config();
> +		if (err) {
> +			pr_err("Failed to allocate configuration arrays.\n");
> +			break;
> +		}
>   
> +		err = mpam_register_irqs();
> +		if (err) {
> +			pr_warn("Failed to register irqs: %d\n", err);
> +			break;
> +		}
> +	} while (0);
>   	mutex_unlock(&mpam_list_lock);
>   	cpus_read_unlock();
>   
> @@ -1861,6 +1976,8 @@ static void mpam_reset_component_locked(struct mpam_component *comp)
>   	might_sleep();
>   	lockdep_assert_cpus_held();
>   
> +	memset(comp->cfg, 0, (mpam_partid_max * sizeof(*comp->cfg)));
And here?
> +
>   	idx = srcu_read_lock(&mpam_srcu);
>   	list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
>   		msc = vmsc->msc;
> @@ -1963,6 +2080,79 @@ void mpam_enable(struct work_struct *work)
>   		mpam_enable_once();
>   }
>   
> +struct mpam_write_config_arg {
> +	struct mpam_msc_ris *ris;
> +	struct mpam_component *comp;
> +	u16 partid;
> +};
> +
> +static int __write_config(void *arg)
> +{
> +	struct mpam_write_config_arg *c = arg;
> +
> +	mpam_reprogram_ris_partid(c->ris, c->partid, &c->comp->cfg[c->partid]);
> +
> +	return 0;
> +}
> +
> +#define maybe_update_config(cfg, feature, newcfg, member, changes) do { \
> +	if (mpam_has_feature(feature, newcfg) &&			\
> +	    (newcfg)->member != (cfg)->member) {			\
> +		(cfg)->member = (newcfg)->member;			\
> +		cfg->features |= (1 << feature);			\
> +									\
> +		(changes) |= (1 << feature);				\
> +	}								\
> +} while (0)
> +
> +static mpam_features_t mpam_update_config(struct mpam_config *cfg,
> +					  const struct mpam_config *newcfg)
> +{
> +	mpam_features_t changes = 0;
> +
> +	maybe_update_config(cfg, mpam_feat_cpor_part, newcfg, cpbm, changes);
> +	maybe_update_config(cfg, mpam_feat_mbw_part, newcfg, mbw_pbm, changes);
> +	maybe_update_config(cfg, mpam_feat_mbw_max, newcfg, mbw_max, changes);
> +
> +	return changes;
> +}
> +
> +/* TODO: split into write_config/sync_config */
> +/* TODO: add config_dirty bitmap to drive sync_config */
> +int mpam_apply_config(struct mpam_component *comp, u16 partid,
> +		      struct mpam_config *cfg)
> +{
> +	struct mpam_write_config_arg arg;
> +	struct mpam_msc_ris *ris;
> +	struct mpam_vmsc *vmsc;
> +	struct mpam_msc *msc;
> +	int idx;
> +
> +	lockdep_assert_cpus_held();
> +
> +	/* Don't pass in the current config! */
> +	WARN_ON_ONCE(&comp->cfg[partid] == cfg);
> +
> +	if (!mpam_update_config(&comp->cfg[partid], cfg))
> +		return 0;
> +
> +	arg.comp = comp;
> +	arg.partid = partid;
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
> +		msc = vmsc->msc;
> +
> +		list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
> +			arg.ris = ris;
> +			mpam_touch_msc(msc, __write_config, &arg);
> +		}
> +	}
> +	srcu_read_unlock(&mpam_srcu, idx);
> +
> +	return 0;
> +}
> +
>   /*
>    * MSC that are hidden under caches are not created as platform devices
>    * as there is no cache driver. Caches are also special-cased in
> diff --git a/drivers/platform/arm64/mpam/mpam_internal.h b/drivers/platform/arm64/mpam/mpam_internal.h
> index 1a24424b48df..029ec89f56f2 100644
> --- a/drivers/platform/arm64/mpam/mpam_internal.h
> +++ b/drivers/platform/arm64/mpam/mpam_internal.h
> @@ -190,11 +190,7 @@ struct mpam_props {
>   	u16			num_mbwu_mon;
>   };
>   
> -static inline bool mpam_has_feature(enum mpam_device_features feat,
> -				    struct mpam_props *props)
> -{
> -	return (1 << feat) & props->features;
> -}
> +#define mpam_has_feature(_feat, x)	((1 << (_feat)) & (x)->features)
>   
>   static inline void mpam_set_feature(enum mpam_device_features feat,
>   				    struct mpam_props *props)
> @@ -225,6 +221,17 @@ struct mpam_class {
>   	struct mpam_garbage	garbage;
>   };
>   
> +struct mpam_config {
> +	/* Which configuration values are valid. 0 is used for reset */
> +	mpam_features_t		features;
> +
> +	u32	cpbm;
> +	u32	mbw_pbm;
> +	u16	mbw_max;
> +
> +	struct mpam_garbage	garbage;
> +};
> +
>   struct mpam_component {
>   	u32			comp_id;
>   
> @@ -233,6 +240,12 @@ struct mpam_component {
>   
>   	cpumask_t		affinity;
>   
> +	/*
> +	 * Array of configuration values, indexed by partid.
> +	 * Read from cpuhp callbacks, hold the cpuhp lock when writing.
> +	 */
> +	struct mpam_config	*cfg;
> +
>   	/* member of mpam_class:components */
>   	struct list_head	class_list;
>   
> @@ -297,6 +310,9 @@ extern u8 mpam_pmg_max;
>   void mpam_enable(struct work_struct *work);
>   void mpam_disable(struct work_struct *work);
>   
> +int mpam_apply_config(struct mpam_component *comp, u16 partid,
> +		      struct mpam_config *cfg);
> +
>   int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
>   				   cpumask_t *affinity);
>   

-- 
Thanks,

Ben