Re: [PATCH 1/2] perf/x86/intel: Fix redundant branch type check in intel_pmu_lbr_filter()

[Mi, Dapeng]

On 4/30/2026 4:58 AM, Chen, Zide wrote:
>
> On 4/13/2026 7:14 PM, Dapeng Mi wrote:
>> In intel_pmu_lbr_filter(), the 'type' variable is bitwise ORed with
>> 'to_plm' (which contains X86_BR_USER and/or X86_BR_KERNEL bits). Because
>> of this, 'type' can never equal X86_BR_NONE (0) after the assignment.
> Nit: In legacy LBR case, it could if get_branch_type() returns X86_BR_NONE.

Yeah, it's correct and need to change the description slightly.

Thanks.


>
>> As a result, the subsequent check 'if (type == X86_BR_NONE)' is dead code
>> and the entries with X86_BR_NONE type would not be skipped eventually.
>>
>> Correct this by masking out the X86_BR_KERNEL and X86_BR_USER bits
>> before performing the X86_BR_NONE comparison.
>>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Fixes: 47125db27e47 ("perf/x86/intel/lbr: Support Architectural LBR")
>> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>> ---
>>  arch/x86/events/intel/lbr.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
>> index 72f2adcda7c6..16977e4c6f8a 100644
>> --- a/arch/x86/events/intel/lbr.c
>> +++ b/arch/x86/events/intel/lbr.c
>> @@ -1245,7 +1245,7 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
>>  		}
>>  
>>  		/* if type does not correspond, then discard */
>> -		if (type == X86_BR_NONE || (br_sel & type) != type) {
>> +		if ((type & ~X86_BR_PLM) == X86_BR_NONE || (br_sel & type) != type) {
>>  			cpuc->lbr_entries[i].from = 0;
>>  			compress = true;
>>  		}