Re: [PATCH] Revert "perf tools: Fix PMU term format max value calculation"

[Jiri Olsa]

ping

thanks,
jirka

On Wed, Oct 03, 2018 at 09:20:46AM +0200, Jiri Olsa wrote:
> This reverts commit ac0e2cd555373ae6f8f3a3ad3fbbf5b6d1e7aaaa.
> 
> Michael reported an issue with oversized terms values assignment
> and I noticed there was actually a misunderstanding of the max
> value check in the past.
> 
> The above commit's changelog says:
> 
>   If bit 21 is set, there is parsing issues as below.
> 
>     $ perf stat -a -e uncore_qpi_0/event=0x200002,umask=0x8/
>     event syntax error: '..pi_0/event=0x200002,umask=0x8/'
>                                       \___ value too big for format, maximum is 511
> 
> But there's no issue there, because the event value is distributed
> along the value defined by the format. Even if the format defines
> separated bit, the value is treated as a continual number, which
> should follow the format definition.
> 
> In above case it's 9-bit value with last bit separated:
>   $ cat uncore_qpi_0/format/event
>   config:0-7,21
> 
> Hence the value 0x200002 is correctly reported as format violation,
> because it exceeds 9 bits. It should have been 0x102 instead, which
> sets the 9th bit - the bit 21 of the format.
> 
>   $ perf stat -vv -a -e uncore_qpi_0/event=0x102,umask=0x8/
>   Using CPUID GenuineIntel-6-2D
>   ...
>   ------------------------------------------------------------
>   perf_event_attr:
>     type                             10
>     size                             112
>     config                           0x200802
>     sample_type                      IDENTIFIER
>   ...
> 
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Kan Liang <kan.liang@xxxxxxxxx>
> Reported-by: Michael Petlan <mpetlan@xxxxxxxxxx>
> Link: http://lkml.kernel.org/n/tip-icxq7a1r66lusm3ahaimekis@xxxxxxxxxxxxxx
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/perf/util/pmu.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index afd68524ffa9..7799788f662f 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -930,13 +930,14 @@ static void pmu_format_value(unsigned long *format, __u64 value, __u64 *v,
>  
>  static __u64 pmu_format_max_value(const unsigned long *format)
>  {
> -	__u64 w = 0;
> -	int fbit;
> -
> -	for_each_set_bit(fbit, format, PERF_PMU_FORMAT_BITS)
> -		w |= (1ULL << fbit);
> +	int w;
>  
> -	return w;
> +	w = bitmap_weight(format, PERF_PMU_FORMAT_BITS);
> +	if (!w)
> +		return 0;
> +	if (w < 64)
> +		return (1ULL << w) - 1;
> +	return -1;
>  }
>  
>  /*
> -- 
> 2.17.1
>