From:   Florian Weimer <fw@deneb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        "H . Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
        linux-api@vger.kernel.org,
        Christian Brauner <christian.brauner@ubuntu.com>,
        carlos@redhat.com
Subject: Re: [RFC PATCH] rseq: x86: implement abort-at-ip extension
References: <20220107170302.8325-1-mathieu.desnoyers@efficios.com>
Date:   Fri, 07 Jan 2022 20:31:24 +0100
In-Reply-To: <20220107170302.8325-1-mathieu.desnoyers@efficios.com> (Mathieu
        Desnoyers's message of "Fri, 7 Jan 2022 12:03:02 -0500")
Message-ID: <87a6g7ny0j.fsf@mid.deneb.enyo.de>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

* Mathieu Desnoyers:

> Allow rseq critical section abort handlers to optionally figure out at
> which instruction pointer the rseq critical section was aborted.
>
> This allows implementing rseq critical sections containing loops, in
> which case the commit side-effect cannot be the last instruction. This
> is useful to implement adaptative mutexes aware of preemption in
> user-space. (see [1])

Could you write the program counter to the rseq area instead?  This
would avoid discussing which register to clobber.

Thanks,
Florian