Re: [PATCH 2/2] x86/resctrl: Support CPUID enumeration of MBM counter width

[Reinette Chatre]

Hi Borislav,

On 4/29/2020 11:11 AM, Borislav Petkov wrote:
> On Wed, Apr 01, 2020 at 10:51:02AM -0700, Reinette Chatre wrote:
>> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
>> index 4cdb123ff66a..8552d2fadc15 100644
>> --- a/arch/x86/kernel/cpu/common.c
>> +++ b/arch/x86/kernel/cpu/common.c
>> @@ -856,6 +856,8 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>>  
>>  static void init_cqm(struct cpuinfo_x86 *c)
>>  {
>> +	c->x86_cache_mbm_width_offset = -1;
>> +
>>  	if (!cpu_has(c, X86_FEATURE_CQM_LLC)) {
>>  		c->x86_cache_max_rmid  = -1;
>>  		c->x86_cache_occ_scale = -1;
>> @@ -875,6 +877,9 @@ static void init_cqm(struct cpuinfo_x86 *c)
>>  
>>  		c->x86_cache_max_rmid  = ecx;
>>  		c->x86_cache_occ_scale = ebx;
>> +		/* EAX contents is only defined for Intel CPUs */
>> +		if (c->x86_vendor == X86_VENDOR_INTEL)
>> +			c->x86_cache_mbm_width_offset = eax & 0xff;
> 
> Remind me again pls why is all this RDT stuff replicated per CPU instead
> of it being properly detected somewhere down in resctrl_late_init()?
> 
> Looking at get_rdt_resources(), it kinda wants to have that in there
> too?
> 
> IOW, how about moving all that gunk in init_cqm() to resctrl/ where it
> truly belongs? Doesn't have to be this patchset but this patchset can
> start moving it...

I am not familiar with the history to clarify to you why the RDT feature
enumeration is not consistent. Even so, there was an effort to
consolidate this in [1] but it was found to go against the goal of
centralizing the CPUID information [2] and was not pursued further. I
would be happy to revisit this if this is the direction that you prefer.
This would essentially be resubmitting [1] though. Do you expect that
this change would receive a different reception at this time?

Thank you

Reinette


[1]
https://lore.kernel.org/lkml/1560705250-211820-2-git-send-email-fenghua.yu@xxxxxxxxx/

[2]
https://lore.kernel.org/lkml/alpine.DEB.2.21.1906162141301.1760@xxxxxxxxxxxxxxxxxxxxxxx/