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

Reinette Chatre
2022-10-25T23:47:44Z

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@amd.com>
> ---
> 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