Re: [PATCH v7 07/12] x86/resctrl: Add sysfs interface to read mbm_total_bytes event configuration

[Reinette Chatre]

Hi Babu,

On 10/17/2022 3:26 PM, Babu Moger wrote:
> The current event configuration can be viewed by the user by reading
> the configuration file /sys/fs/resctrl/info/L3_MON/mbm_total_config.
> The event configuration settings are domain specific and will affect all
> the CPUs in the domain.
> 
> Following are the types of events supported:
> ====  ===========================================================
> Bits   Description
> ====  ===========================================================
> 6      Dirty Victims from the QOS domain to all types of memory
> 5      Reads to slow memory in the non-local NUMA domain
> 4      Reads to slow memory in the local NUMA domain
> 3      Non-temporal writes to non-local NUMA domain
> 2      Non-temporal writes to local NUMA domain
> 1      Reads to memory in the non-local NUMA domain
> 0      Reads to memory in the local NUMA domain
> ====  ===========================================================
> 
> By default, the mbm_total_bytes configuration is set to 0x7f to count
> all the event types.
> 
> For example:
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_total_config
>     0=0x7f;1=0x7f;2=0x7f;3=0x7f
> 
>     In this case, the event mbm_total_bytes is currently configured
>     with 0x7f on domains 0 to 3.
> 
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     |    3 +
>  arch/x86/kernel/cpu/resctrl/internal.h |    2 +
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |   76 ++++++++++++++++++++++++++++++++
>  3 files changed, 81 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 46813b1c50c2..758c5d7553a4 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -826,6 +826,9 @@ static __init bool get_rdt_mon_resources(void)
>  	if (!rdt_mon_features)
>  		return false;
>  
> +	if (mon_configurable)
> +		mbm_config_rftype_init();
> +

Please move this to be within rdt_get_mon_l3_config().

>  	return !rdt_get_mon_l3_config(r, mon_configurable);
>  }
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index b458f768f30c..326a1b582f38 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -15,6 +15,7 @@
>  #define MSR_IA32_MBA_THRTL_BASE		0xd50
>  #define MSR_IA32_MBA_BW_BASE		0xc0000200
>  #define MSR_IA32_SMBA_BW_BASE		0xc0000280
> +#define MSR_IA32_EVT_CFG_BASE		0xc0000400
>  
>  #define MSR_IA32_QM_CTR			0x0c8e
>  #define MSR_IA32_QM_EVTSEL		0x0c8d
> @@ -541,5 +542,6 @@ bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
>  void __check_limbo(struct rdt_domain *d, bool force_free);
>  void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
>  void __init thread_throttle_mode_init(void);
> +void __init mbm_config_rftype_init(void);
>  
>  #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 5f0ef1bf4c78..0982845594d0 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1423,6 +1423,67 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +struct mon_config_info {
> +	u32 evtid;
> +	u32 mon_config;
> +};
> +
> +static void mon_event_config_read(void *info)
> +{
> +	struct mon_config_info *mon_info = info;
> +	u32 h, msr_index;
> +
> +	switch (mon_info->evtid) {
> +	case QOS_L3_MBM_TOTAL_EVENT_ID:
> +		msr_index = 0;
> +		break;
> +	case QOS_L3_MBM_LOCAL_EVENT_ID:
> +		msr_index = 1;
> +		break;
> +	default:
> +		/* Not expected to come here */
> +		return;
> +	}
> +
> +	rdmsr(MSR_IA32_EVT_CFG_BASE + msr_index, mon_info->mon_config, h);
> +}
> +
> +static void mondata_config_read(struct rdt_domain *d, struct mon_config_info *mon_info)
> +{
> +	smp_call_function_any(&d->cpu_mask, mon_event_config_read, mon_info, 1);
> +}
> +
> +static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid)
> +{
> +	struct mon_config_info mon_info = {0};
> +	struct rdt_domain *dom;
> +	bool sep = false;
> +
> +	list_for_each_entry(dom, &r->domains, list) {

This is done with no protection ... I do not see anything preventing last CPU of
a domain going offline around this time taking this domain with it while this code
still tries to access its members.

I think all of this needs protection with rdtgroup_mutex.

> +		if (sep)
> +			seq_puts(s, ";");
> +
> +		mon_info.evtid = evtid;
> +		mondata_config_read(dom, &mon_info);
> +
> +		seq_printf(s, "%d=0x%02x", dom->id, mon_info.mon_config);

It does not seem robust to me to use printf field width to manage the data
returned from hardware. At this time bits 0 - 6 are supported by hardware ...
what happens if hardware starts using bit 7 for something? 
It seems to me that the mask introduced later needs to be pulled here to
ensure that only the valid bits are handled.

> +		sep = true;
> +	}
> +	seq_puts(s, "\n");
> +
> +	return 0;
> +}
> +
> +static int mbm_total_config_show(struct kernfs_open_file *of,
> +				 struct seq_file *seq, void *v)
> +{
> +	struct rdt_resource *r = of->kn->parent->priv;
> +
> +	mbm_config_show(seq, r, QOS_L3_MBM_TOTAL_EVENT_ID);
> +
> +	return 0;
> +}
> +
>  /* rdtgroup information files for one cache resource. */
>  static struct rftype res_common_files[] = {
>  	{
> @@ -1521,6 +1582,12 @@ static struct rftype res_common_files[] = {
>  		.seq_show	= max_threshold_occ_show,
>  		.fflags		= RF_MON_INFO | RFTYPE_RES_CACHE,
>  	},
> +	{
> +		.name		= "mbm_total_config",
> +		.mode		= 0644,
> +		.kf_ops		= &rdtgroup_kf_single_ops,
> +		.seq_show	= mbm_total_config_show,
> +	},

Please only make mode writable when there is support for it.

>  	{
>  		.name		= "cpus",
>  		.mode		= 0644,
> @@ -1627,6 +1694,15 @@ void __init thread_throttle_mode_init(void)
>  	rft->fflags = RF_CTRL_INFO | RFTYPE_RES_MB;
>  }
>  
> +void __init mbm_config_rftype_init(void)
> +{
> +	struct rftype *rft;
> +
> +	rft = rdtgroup_get_rftype_by_name("mbm_total_config");
> +	if (rft)
> +		rft->fflags = RF_MON_INFO | RFTYPE_RES_CACHE;
> +}
> +
>  /**
>   * rdtgroup_kn_mode_restrict - Restrict user access to named resctrl file
>   * @r: The resource group with which the file is associated.
> 
> 


Reinette