linux-kernel - Re: [PATCH] rseq: update kernel fields in lockstep with CONFIG_DEBUG

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Message-ID: <26dba55c-eb09-4e9e-8460-8adbf75e32cd@efficios.com>
Date: Mon, 24 Feb 2025 15:40:31 -0500
From: Michael Jeanson <mjeanson@...icios.com>
To: Ingo Molnar <mingo@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rseq: update kernel fields in lockstep with
 CONFIG_DEBUG_RSEQ

On 2025-02-22 09:12, Ingo Molnar wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
>>>> -	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
>>>> -	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
>>>> -	unsafe_put_user(node_id, &rseq->node_id, efault_end);
>>>> -	unsafe_put_user(mm_cid, &rseq->mm_cid, efault_end);
>>>> +
>>>> +	unsafe_rseq_set_field(t, cpu_id_start, cpu_id, efault_end);
>>>> +	unsafe_rseq_set_field(t, cpu_id, cpu_id, efault_end);
>>>> +	unsafe_rseq_set_field(t, node_id, node_id, efault_end);
>>>> +	unsafe_rseq_set_field(t, mm_cid, mm_cid, efault_end);
>>>
>>> Could we please name the new wrapper rseq_unsafe_put_user(), to make it
>>> clear it's a wrapper around unsafe_put_user()?
>>
>> If we do this then need to make sure the order of arguments becomes
>> similar to unsafe_put_user for consistency.
> 
> Absolutely.
> 
>> I always find it odd that the "source" argument comes first and
>> the "destination" argument comes second in all put_user() APIs,
>> compared to memcpy, WRITE_ONCE() and all assignments (e.g.
>> operator "=" LHS vs RHS). Choosing a different argument order
>> therefore made sense with a naming different from "*put_user",
>> but not so much if we use a derived naming.
> 
> Yeah, put_user()'s oddity is a random historic idiosyncrasy that we 
> want to preserve in derived naming to reduce the potential for 
> confusion.

Would that be ok?

  rseq_unsafe_put_user(t, value, field, error_label)

> 
> Thanks,
> 
> 	Ingo