Re: [PATCH 23/33] arm_mpam: Allow configuration to be applied and restored during cpu online

Ben Horgan
2025-11-13T17:15:02Z

Hi Gavin,

On 11/9/25 22:59, Gavin Shan wrote:
> Hi Ben
>
> On 11/7/25 10:34 PM, Ben Horgan wrote:
>> From: James Morse <james.morse@arm.com>
>>
>> When CPUs come online the MSC's original configuration should be
>> restored.
>>
>> Add struct mpam_config to hold the configuration. This has a bitmap of
>> features that were modified. Once the maximum partid is known, allocate
>> a configuration array for each component, and reprogram each RIS
>> configuration from this.
>>
>> CC: Dave Martin <Dave.Martin@arm.com>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> Cc: Shaopeng Tan (Fujitsu) tan.shaopeng@fujitsu.com
>> Cc: Peter Newman peternewman@google.com
>> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
>> ---
>> Changes since v3:
>> Drop tags
>> Fix component reset, otherwise cpbm wrong and controls not set.
>> Add a cfg_lock to guard configuration of an msc
>> ---
>>   drivers/resctrl/mpam_devices.c  | 268 ++++++++++++++++++++++++++++++--
>>   drivers/resctrl/mpam_internal.h |  27 ++++
>>   2 files changed, 280 insertions(+), 15 deletions(-)
>>
>
> With the following comments addressed:
>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/
>> mpam_devices.c
>> index 3a0ad8d93fff..8b0944bdaf28 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -144,6 +144,16 @@ static void mpam_free_garbage(void)
>>       }
>>   }
>>   +/*
>> + * Once mpam is enabled, new requestors cannot further reduce the
>> available
>> + * partid. Assert that the size is fixed, and new requestors will be
>> turned
>> + * away.
>> + */
>> +static void mpam_assert_partid_sizes_fixed(void)
>> +{
>> +    WARN_ON_ONCE(!partid_max_published);
>> +}
>> +
>
> Would be worthy to be a online function.

Assuming you mean 'inline'. I don't think it really matters but I'll
leave it as is so that WARN_ON_ONCE() only ever gives one warning.

>
>>   static u32 __mpam_read_reg(struct mpam_msc *msc, u16 reg)
>>   {
>>       WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc-
>> >accessibility));
>> @@ -343,6 +353,7 @@ mpam_component_alloc(struct mpam_class *class, int
>> id)
>>       return comp;
>>   }
>>   +static void __destroy_component_cfg(struct mpam_component *comp);
>>   static void mpam_class_destroy(struct mpam_class *class);
>>     static void mpam_component_destroy(struct mpam_component *comp)
>> @@ -351,6 +362,8 @@ static void mpam_component_destroy(struct
>> mpam_component *comp)
>>         lockdep_assert_held(&mpam_list_lock);
>>   +    __destroy_component_cfg(comp);
>> +
>>       list_del_rcu(&comp->class_list);
>>       add_to_garbage(comp);
>>   @@ -820,31 +833,59 @@ 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)
>>   {
>>       struct mpam_msc *msc = ris->vmsc->msc;
>>       struct mpam_props *rprops = &ris->props;
>>   -    WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
>> -
>>       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) &&
>> +        mpam_has_feature(mpam_feat_cpor_part, cfg)) {
>> +        if (cfg->reset_cpbm)
>> +            mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM,
>> +                          rprops->cpbm_wd);
>> +        else
>> +            mpam_write_partsel_reg(msc, CPBM, cfg->cpbm);
>> +    }
>
> {} is needed by 'if (cfg->reset_cpbm)'

Changed to be one line.

>
>>   -    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) &&
>> +        mpam_has_feature(mpam_feat_mbw_part, cfg)) {
>> +        if (cfg->reset_mbw_pbm)
>> +            mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM,
>> +                          rprops->mbw_pbm_bits);
>> +        else
>> +            mpam_write_partsel_reg(msc, MBW_PBM, cfg->mbw_pbm);
>> +    }
>>
>
> { } is need by 'if (cfg->reset_mbw_pbm)'

Changed to be one line.

>
>> -    if (mpam_has_feature(mpam_feat_mbw_min, rprops))
>> +    if (mpam_has_feature(mpam_feat_mbw_min, rprops) &&
>> +        mpam_has_feature(mpam_feat_mbw_min, cfg))
>>           mpam_write_partsel_reg(msc, MBW_MIN, 0);
>>   -    if (mpam_has_feature(mpam_feat_mbw_max, rprops))
>> -        mpam_write_partsel_reg(msc, MBW_MAX, MPAMCFG_MBW_MAX_MAX);
>> +    if (mpam_has_feature(mpam_feat_mbw_max, rprops) &&
>> +        mpam_has_feature(mpam_feat_mbw_max, cfg)) {
>> +        if (cfg->reset_mbw_max)
>> +            mpam_write_partsel_reg(msc, MBW_MAX, MPAMCFG_MBW_MAX_MAX);
>> +        else
>> +            mpam_write_partsel_reg(msc, MBW_MAX, cfg->mbw_max);
>> +    }
>>         mutex_unlock(&msc->part_sel_lock);
>>   }
>>   +static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
>> +{
>> +    *reset_cfg = (struct mpam_config) {
>> +        .reset_cpbm = true,
>> +        .reset_mbw_pbm = true,
>> +        .reset_mbw_max = true,
>> +    };
>> +    bitmap_fill(reset_cfg->features, MPAM_FEATURE_LAST);
>> +}
>> +
>>   /*
>>    * Called via smp_call_on_cpu() to prevent migration, while still being
>>    * pre-emptible. Caller must hold mpam_srcu.
>> @@ -852,16 +893,19 @@ static void mpam_reset_ris_partid(struct
>> mpam_msc_ris *ris, u16 partid)
>>   static int mpam_reset_ris(void *arg)
>>   {
>>       u16 partid, partid_max;
>> +    struct mpam_config reset_cfg;
>>       struct mpam_msc_ris *ris = arg;
>>         if (ris->in_reset_state)
>>           return 0;
>>   +    mpam_init_reset_cfg(&reset_cfg);
>> +
>>       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);
>> +        mpam_reprogram_ris_partid(ris, partid, &reset_cfg);
>>         return 0;
>>   }
>> @@ -894,6 +938,7 @@ static void mpam_reset_msc(struct mpam_msc *msc,
>> bool online)
>>   {
>>       struct mpam_msc_ris *ris;
>>   +    mutex_lock(&msc->cfg_lock);
>>       list_for_each_entry_srcu(ris, &msc->ris, msc_list,
>> srcu_read_lock_held(&mpam_srcu)) {
>>           mpam_touch_msc(msc, &mpam_reset_ris, ris);
>>   @@ -903,6 +948,61 @@ static void mpam_reset_msc(struct mpam_msc
>> *msc, bool online)
>>            */
>>           ris->in_reset_state = online;
>>       }
>> +    mutex_unlock(&msc->cfg_lock);
>> +}
>> +
>> +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;
>> +}
>> +
>> +static void mpam_reprogram_msc(struct mpam_msc *msc)
>> +{
>> +    u16 partid;
>> +    bool reset;
>> +    struct mpam_config *cfg;
>> +    struct mpam_msc_ris *ris;
>> +    struct mpam_write_config_arg arg;
>> +
>> +    /*
>> +     * No lock for mpam_partid_max as partid_max_published has been
>> +     * set by mpam_enabled(), so the values can no longer change.
>> +     */
>> +    mpam_assert_partid_sizes_fixed();
>> +
>> +    mutex_lock(&msc->cfg_lock);
>> +    list_for_each_entry_srcu(ris, &msc->ris, msc_list,
>> +                 srcu_read_lock_held(&mpam_srcu)) {
>> +        if (!mpam_is_enabled() && !ris->in_reset_state) {
>> +            mpam_touch_msc(msc, &mpam_reset_ris, ris);
>> +            ris->in_reset_state = true;
>> +            continue;
>> +        }
>> +
>> +        arg.comp = ris->vmsc->comp;
>> +        arg.ris = ris;
>> +        reset = true;
>> +        for (partid = 0; partid <= mpam_partid_max; partid++) {
>> +            cfg = &ris->vmsc->comp->cfg[partid];
>> +            if (!bitmap_empty(cfg->features, MPAM_FEATURE_LAST))
>> +                reset = false;
>> +
>
> s/!bitmap_empty()/!bitmap_full (?)

This is checking if there is any work for the configuration to do and so
checking if there are any feature bits set, !bitmap_empty(), is the
correct thing to do.

>
>> +            arg.partid = partid;
>> +            mpam_touch_msc(msc, __write_config, &arg);
>> +        }
>> +        ris->in_reset_state = reset;
>> +    }
>> +    mutex_unlock(&msc->cfg_lock);
>>   }
>>     static void _enable_percpu_irq(void *_irq)
>> @@ -926,7 +1026,7 @@ 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);
>>       }
>>         return 0;
>> @@ -1125,6 +1225,9 @@ static struct mpam_msc
>> *do_mpam_msc_drv_probe(struct platform_device *pdev)
>>       if (err)
>>           return ERR_PTR(err);
>>       err = devm_mutex_init(dev, &msc->error_irq_lock);
>> +    if (err)
>> +        return ERR_PTR(err);
>> +    err = devm_mutex_init(dev, &msc->cfg_lock);
>>       if (err)
>>           return ERR_PTR(err);
>>       mpam_mon_sel_lock_init(msc);
>> @@ -1585,6 +1688,70 @@ static void mpam_unregister_irqs(void)
>>       }
>>   }
>>   +static void __destroy_component_cfg(struct mpam_component *comp)
>> +{
>> +    add_to_garbage(comp->cfg);
>> +}
>> +
>> +static void mpam_reset_component_cfg(struct mpam_component *comp)
>> +{
>> +    int i;
>> +    struct mpam_props *cprops = &comp->class->props;
>> +
>> +    mpam_assert_partid_sizes_fixed();
>> +
>> +    if (!comp->cfg)
>> +        return;
>> +
>> +    for (i = 0; i <= mpam_partid_max; i++) {
>> +        comp->cfg[i] = (struct mpam_config) {};
>> +        bitmap_fill(comp->cfg[i].features, MPAM_FEATURE_LAST);
>> +        bitmap_set((unsigned long *)&comp->cfg[i].cpbm, 0, cprops-
>> >cpbm_wd);
>> +        bitmap_set((unsigned long *)&comp->cfg[i].mbw_pbm, 0, cprops-
>> >mbw_pbm_bits);
>> +        bitmap_set((unsigned long *)&comp->cfg[i].mbw_max, 16 -
>> cprops->bwa_wd, cprops->bwa_wd);
>> +    }
>> +}
>> +
>> +static int __allocate_component_cfg(struct mpam_component *comp)
>> +{
>> +    mpam_assert_partid_sizes_fixed();
>> +
>> +    if (comp->cfg)
>> +        return 0;
>> +
>> +    comp->cfg = kcalloc(mpam_partid_max + 1, sizeof(*comp->cfg),
>> GFP_KERNEL);
>> +    if (!comp->cfg)
>> +        return -ENOMEM;
>> +
>> +    /*
>> +     * The array is free()d in one go, so only cfg[0]'s structure needs
>> +     * to be initialised.
>> +     */
>> +    init_garbage(&comp->cfg[0].garbage);
>> +
>> +    mpam_reset_component_cfg(comp);
>> +
>> +    return 0;
>> +}
>> +
>> +static int mpam_allocate_config(void)
>> +{
>> +    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) {
>> +            int err = __allocate_component_cfg(comp);
>> +            if (err)
>> +                return err;
>> +        }
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static void mpam_enable_once(void)
>>   {
>>       int err;
>> @@ -1604,15 +1771,25 @@ 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();
>> +        err = mpam_register_irqs();
>> +        if (err) {
>> +            pr_warn("Failed to register irqs: %d\n", err);
>> +            break;
>> +        }
>>   +        err = mpam_allocate_config();
>> +        if (err) {
>> +            pr_err("Failed to allocate configuration arrays.\n");
>> +            break;
>> +        }
>> +    } while (0);
>>       mutex_unlock(&mpam_list_lock);
>>       cpus_read_unlock();
>>         if (err) {
>> -        pr_warn("Failed to register irqs: %d\n", err);
>>           mpam_disable_reason = "Failed to enable.";
>>           schedule_work(&mpam_broken_work);
>>           return;
>> @@ -1632,6 +1809,9 @@ static void mpam_reset_component_locked(struct
>> mpam_component *comp)
>>       struct mpam_vmsc *vmsc;
>>         lockdep_assert_cpus_held();
>> +    mpam_assert_partid_sizes_fixed();
>> +
>> +    mpam_reset_component_cfg(comp);
>>         guard(srcu)(&mpam_srcu);
>>       list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
>> @@ -1732,6 +1912,64 @@ void mpam_enable(struct work_struct *work)
>>           mpam_enable_once();
>>   }
>>   +#define maybe_update_config(cfg, feature, newcfg, member, changes)
>> do { \
>> +    if (mpam_has_feature(feature, newcfg) &&            \
>> +        (newcfg)->member != (cfg)->member) {            \
>> +        (cfg)->member = (newcfg)->member;            \
>> +        mpam_set_feature(feature, cfg);                \
>> +                                    \
>> +        (changes) = true;                    \
>> +    }                                \
>> +} while (0)
>> +
>> +static bool mpam_update_config(struct mpam_config *cfg,
>> +                   const struct mpam_config *newcfg)
>> +{
>> +    bool has_changes = false;
>> +
>> +    maybe_update_config(cfg, mpam_feat_cpor_part, newcfg, cpbm,
>> has_changes);
>> +    maybe_update_config(cfg, mpam_feat_mbw_part, newcfg, mbw_pbm,
>> has_changes);
>> +    maybe_update_config(cfg, mpam_feat_mbw_max, newcfg, mbw_max,
>> has_changes);
>> +
>> +    return has_changes;
>> +}
>> +
>> +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;
>> +
>> +    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;
>> +
>> +    guard(srcu)(&mpam_srcu);
>> +    list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
>> +                 srcu_read_lock_held(&mpam_srcu)) {
>> +        msc = vmsc->msc;
>> +
>> +        mutex_lock(&msc->cfg_lock);
>> +        list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
>> +                     srcu_read_lock_held(&mpam_srcu)) {
>> +            arg.ris = ris;
>> +            mpam_touch_msc(msc, __write_config, &arg);
>> +        }
>> +        mutex_unlock(&msc->cfg_lock);
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static int __init mpam_msc_driver_init(void)
>>   {
>>       if (!system_supports_mpam())
>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/
>> mpam_internal.h
>> index c6937161877a..842d32f148b5 100644
>> --- a/drivers/resctrl/mpam_internal.h
>> +++ b/drivers/resctrl/mpam_internal.h
>> @@ -91,6 +91,9 @@ struct mpam_msc {
>>        */
>>       struct mutex        part_sel_lock;
>>   +    /* cfg_lock protects the msc configuration. */
>> +    struct mutex        cfg_lock;
>> +
>>       /*
>>        * mon_sel_lock protects access to the MSC hardware registers
>> that are
>>        * affected by MPAMCFG_MON_SEL, and the mbwu_state.
>> @@ -180,6 +183,21 @@ struct mpam_class {
>>       struct mpam_garbage    garbage;
>>   };
>>   +struct mpam_config {
>> +    /* Which configuration values are valid. */
>> +    DECLARE_BITMAP(features, MPAM_FEATURE_LAST);
>> +
>> +    u32    cpbm;
>> +    u32    mbw_pbm;
>> +    u16    mbw_max;
>> +
>> +    bool    reset_cpbm;
>> +    bool    reset_mbw_pbm;
>> +    bool    reset_mbw_max;
>> +
>> +    struct mpam_garbage    garbage;
>> +};
>> +
>>   struct mpam_component {
>>       u32            comp_id;
>>   @@ -188,6 +206,12 @@ 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;
>>   @@ -247,6 +271,9 @@ 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,
> Gavin
>

Thanks,

Ben