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

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Message-ID: <Z7nbYcdRKXspX8o2@gmail.com>
Date: Sat, 22 Feb 2025 15:12:49 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Michael Jeanson <mjeanson@...icios.com>,
	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


* 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.

Thanks,

	Ingo