Hi Reinette,
On 1/3/24 12:38, Reinette Chatre wrote:
> Hi Babu,
>
> 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.
--
Thanks
Babu Moger
