Re: [PATCH v2 1/3] perf: Add perf_event_attr::bp_priv

[Will Deacon <will@kernel.org>]

On Fri, Jun 21, 2024 at 03:39:08PM +0800, Tiezhu Yang wrote:
> Add a member "bp_priv" at the end of the uapi struct perf_event_attr
> to make a bridge between ptrace and hardware breakpoint.
> 
> This is preparation for later patch on some archs such as ARM, ARM64
> and LoongArch which have privilege level of breakpoint.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  include/uapi/linux/perf_event.h | 3 +++
>  kernel/events/hw_breakpoint.c   | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 3a64499b0f5d..f9f917e854e6 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -379,6 +379,7 @@ enum perf_event_read_format {
>  #define PERF_ATTR_SIZE_VER6	120	/* add: aux_sample_size */
>  #define PERF_ATTR_SIZE_VER7	128	/* add: sig_data */
>  #define PERF_ATTR_SIZE_VER8	136	/* add: config3 */
> +#define PERF_ATTR_SIZE_VER9	144	/* add: bp_priv */
>  
>  /*
>   * Hardware event_id to monitor via a performance monitoring event:
> @@ -522,6 +523,8 @@ struct perf_event_attr {
>  	__u64	sig_data;
>  
>  	__u64	config3; /* extension of config2 */
> +
> +	__u8	bp_priv; /* privilege level of breakpoint */
>  };

Why are we extending the user ABI for this? Perf events already have the
privilege encoded (indirectly) by the exclude_{user,kernel,hv} fields in
'struct perf_event_attr'.

Will