Re: [PATCH v2 2/2] x86/resctrl: Remove hard-coded memory bandwidth event configuration

[Reinette Chatre]

Hi Babu,

On 12/12/2023 10:02 AM, Babu Moger wrote:
> If the BMEC (Bandwidth Monitoring Event Configuration) feature is
> supported, the bandwidth events can be configured. The maximum supported
> bandwidth bitmask can be determined by following CPUID command.
> 
> CPUID_Fn80000020_ECX_x03 [Platform QoS Monitoring Bandwidth Event
> Configuration] Read-only. Reset: 0000_007Fh.
> Bits	Description
> 31:7	Reserved
>  6:0	Identifies the bandwidth sources that can be tracked.
> 
> The bandwidth sources can change with the processor generations.
> Currently, this information is hard-coded. Remove the hard-coded value
> and detect using CPUID command. Also print the valid bitmask when the
> user tries to configure invalid value.
> 
> The CPUID details are documentation in the PPR listed below [1].
> [1] Processor Programming Reference (PPR) Vol 1.1 for AMD Family 19h Model
> 11h B1 - 55901 Rev 0.25.
> 
> Fixes: dc2a3e857981 ("x86/resctrl: Add interface to read mbm_total_bytes_config")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> 
> ---
> v2: Earlier Sent as a part of ABMC feature.
>     https://lore.kernel.org/lkml/20231201005720.235639-1-babu.moger@xxxxxxx/
>     But this is not related to ABMC. Sending it separate now.
>     Removed the global resctrl_max_evt_bitmask. Added event_mask as part of
>     the resource.
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h |    5 ++---
>  arch/x86/kernel/cpu/resctrl/monitor.c  |    6 ++++++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |   18 ++++++++++--------
>  3 files changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index d2979748fae4..3e2f505614d8 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -50,9 +50,6 @@
>  /* Dirty Victims to All Types of Memory */
>  #define DIRTY_VICTIMS_TO_ALL_MEM	BIT(6)
>  
> -/* Max event bits supported */
> -#define MAX_EVT_CONFIG_BITS		GENMASK(6, 0)
> -
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> @@ -394,6 +391,7 @@ struct rdt_parse_data {
>   * @msr_update:		Function pointer to update QOS MSRs
>   * @mon_scale:		cqm counter * mon_scale = occupancy in bytes
>   * @mbm_width:		Monitor width, to detect and correct for overflow.
> + * @event_mask:		Max supported event bitmask.

This is a very generic name and description for this feature. Note that in
resctrl monitoring an "event" is already clear (see members of enum resctrl_event_id)
so a generic type of "event_mask" can easily cause confusion with existing
concept of events. How about "mbm_cfg_mask"? Please also make the description
more detailed - it could include that this is unique to BMEC. 

>   * @cdp_enabled:	CDP state of this resource
>   *
>   * Members of this structure are either private to the architecture
> @@ -408,6 +406,7 @@ struct rdt_hw_resource {
>  				 struct rdt_resource *r);
>  	unsigned int		mon_scale;
>  	unsigned int		mbm_width;
> +	unsigned int		event_mask;
>  	bool			cdp_enabled;
>  };
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index f136ac046851..30bf919edfda 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -813,6 +813,12 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>  		return ret;
>  
>  	if (rdt_cpu_has(X86_FEATURE_BMEC)) {
> +		u32 eax, ebx, ecx, edx;
> +
> +		/* Detect list of bandwidth sources that can be tracked */
> +		cpuid_count(0x80000020, 3, &eax, &ebx, &ecx, &edx);
> +		hw_res->event_mask = ecx;
> +

This has the same issue as I mentioned in V1. Note that this treats
reserved bits as valid values. I think this is a risky thing to do. For example
when this code is run on future hardware the currently reserved bits may have
values with different meaning than what this code uses it for.

>  		if (rdt_cpu_has(X86_FEATURE_CQM_MBM_TOTAL)) {
>  			mbm_total_event.configurable = true;
>  			mbm_config_rftype_init("mbm_total_bytes_config");
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 69a1de92384a..8a1e9fdab974 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1537,17 +1537,14 @@ static void mon_event_config_read(void *info)
>  {
>  	struct mon_config_info *mon_info = info;
>  	unsigned int index;
> -	u64 msrval;
> +	u32 h;
>  
>  	index = mon_event_config_index_get(mon_info->evtid);
>  	if (index == INVALID_CONFIG_INDEX) {
>  		pr_warn_once("Invalid event id %d\n", mon_info->evtid);
>  		return;
>  	}
> -	rdmsrl(MSR_IA32_EVT_CFG_BASE + index, msrval);
> -
> -	/* Report only the valid event configuration bits */
> -	mon_info->mon_config = msrval & MAX_EVT_CONFIG_BITS;
> +	rdmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, h);

I do not think this code needed to be changed. We do not want to treat
reserved bits as valid values. 

>  }
>  
>  static void mondata_config_read(struct rdt_domain *d, struct mon_config_info *mon_info)
> @@ -1557,6 +1554,7 @@ static void mondata_config_read(struct rdt_domain *d, struct mon_config_info *mo
>  
>  static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid)
>  {
> +	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct mon_config_info mon_info = {0};
>  	struct rdt_domain *dom;
>  	bool sep = false;
> @@ -1571,7 +1569,9 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
>  		mon_info.evtid = evtid;
>  		mondata_config_read(dom, &mon_info);
>  
> -		seq_printf(s, "%d=0x%02x", dom->id, mon_info.mon_config);
> +		/* Report only the valid event configuration bits */
> +		seq_printf(s, "%d=0x%02x", dom->id,
> +			   mon_info.mon_config & hw_res->event_mask);
>  		sep = true;
>  	}
>  	seq_puts(s, "\n");
> @@ -1617,12 +1617,14 @@ static void mon_event_config_write(void *info)
>  static int mbm_config_write_domain(struct rdt_resource *r,
>  				   struct rdt_domain *d, u32 evtid, u32 val)
>  {
> +	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct mon_config_info mon_info = {0};
>  	int ret = 0;
>  
>  	/* mon_config cannot be more than the supported set of events */
> -	if (val > MAX_EVT_CONFIG_BITS) {
> -		rdt_last_cmd_puts("Invalid event configuration\n");
> +	if ((val & hw_res->event_mask) != val) {
> +		rdt_last_cmd_printf("Invalid input: The maximum valid bitmask is 0x%02x\n",
> +				    hw_res->event_mask);
>  		return -EINVAL;
>  	}
>  
> 
> 

Reinette