Hi Babu,
On 1/3/2024 1:03 PM, Moger, Babu wrote:
> On 1/3/24 12:38, Reinette Chatre wrote:
>> On 1/2/2024 12:00 PM, Moger, Babu wrote:
>>> On 12/14/23 19:24, Reinette Chatre wrote:
>>>> On 12/12/2023 10:02 AM, Babu Moger wrote:
>>
>>>>> 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.
>>>
>>> Sure. Will use the mask MAX_EVT_CONFIG_BITS.
>>> hw_res->mbm_cfg_mask = ecx & MAX_EVT_CONFIG_BITS;
>>>
>>>>
>>>>> 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.
>>>
>>> The logic is still the same. We don't have access to rdt_hw_resource in
>>> this function. So, I just moved the masking to mbm_config_show while printing.
>>
>> Why do you need access to rdt_hw_resource? This comment is not about the bandwidth
>> events supported by the device but instead the bits used to represent these events.
>> This is the same issue as in rdt_get_mon_l3_config. The above change returns
>> reserved bits as valid while the original code ensured that only bits used for
>> field are returned (through the usage of MAX_EVT_CONFIG_BITS).
>
> We are already saving the valid bits in hw_res->mbm_cfg_mask during the init.
>
> hw_res->mbm_cfg_mask = ecx & MAX_EVT_CONFIG_BITS;
>
> I thought we can use it here directly to mask any unsupported bits. So, I
> re-arranged the code here.
I am not sure where you mean when you say "use it here" since mbm_cfg_mask is not
used in mon_event_config_read(). My comment is related to mon_event_config_read()
that can reasonably be expected to, and thus should, return the current "mon event
config" value and nothing more.
Reinette
