linux-kernel - Re: [PATCH v3 1/3] perf: Add perf_event_attr::bp

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Message-ID: <20240709100304.GA12978@willie-the-truck>
Date: Tue, 9 Jul 2024 11:03:04 +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 v3 1/3] perf: Add perf_event_attr::bp_priv

On Tue, Jul 09, 2024 at 05:55:04PM +0800, Tiezhu Yang wrote:
> When developing hardware watchpoint on LoongArch, we want to set the
> same privilege passed by the ptrace user data, but there is no bridge
> to save this value like bp_addr, bp_type and bp_len. This is a common
> issue for the archs which have privilege level of breakpoint.
> 
> Add a member "bp_priv" which lives in a union on config3 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 | 5 ++++-
>  kernel/events/hw_breakpoint.c   | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 3a64499b0f5d..abe8da7a1f60 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -521,7 +521,10 @@ struct perf_event_attr {
>  	 */
>  	__u64	sig_data;
>  
> -	__u64	config3; /* extension of config2 */
> +	union {
> +		__u8	bp_priv; /* privilege level of breakpoint */
> +		__u64	config3; /* extension of config2 */
> +	};
>  };
>  
>  /*
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index 6c2cb4e4f48d..3ad16b226e4f 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -754,6 +754,7 @@ static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
>  	to->bp_addr = from->bp_addr;
>  	to->bp_type = from->bp_type;
>  	to->bp_len  = from->bp_len;
> +	to->bp_priv = from->bp_priv;
>  	to->disabled = from->disabled;
>  }

Sorry, but I still don't see why we should change uapi for this. As I
have said multiple times, this is unnecessary.

Will