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

[Chen, Zide]

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.

> 
> 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;
>  		}