linux-kernel - Re: [PATCH v2 1/3] perf: Add perf_event_attr::bp

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Message-ID: <20240705103413.GA8971@willie-the-truck>
Date: Fri, 5 Jul 2024 11:34:13 +0100
From: Will Deacon <will@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Mark Rutland <mark.rutland@....com>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] perf: Add perf_event_attr::bp_priv

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@...ngson.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