linux-kernel - Re: [RFC PATCH] rseq: x86: implement abort-at-ip extension

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Message-ID: <87a6g7ny0j.fsf@mid.deneb.enyo.de>
Date:   Fri, 07 Jan 2022 20:31:24 +0100
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        carlos@...hat.com
Subject: Re: [RFC PATCH] rseq: x86: implement abort-at-ip extension

* 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