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

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Message-ID: <6d18e6fc-1d3f-f866-e887-bf5e01fb9368@loongson.cn>
Date: Tue, 9 Jul 2024 20:05:40 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Will Deacon <will@...nel.org>
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 07/09/2024 06:03 PM, Will Deacon wrote:
> 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.

Thanks for your review, I see your point but let us wait
for more comments from perf people.

Thanks,
Tiezhu