linux-kernel - Re: [RFC PATCH for 5.8 3/4] rseq: Introduce RSEQ_FLAG_RELIABLE_CPU

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Date:   Tue, 07 Jul 2020 21:55:31 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Carlos O'Donell <carlos@...hat.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api <linux-api@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Neel Natu <neelnatu@...gle.com>
Subject: Re: [RFC PATCH for 5.8 3/4] rseq: Introduce RSEQ_FLAG_RELIABLE_CPU_ID

* Carlos O'Donell:

> It's not a great fit IMO. Just let the kernel version be the arbiter of
> correctness.

For manual review, sure.  But checking it programmatically does not
yield good results due to backports.  Even those who use the stable
kernel series sometimes pick up critical fixes beforehand, so it's not
reliable possible for a program to say, “I do not want to run on this
kernel because it has a bad version”.  We had a recent episode of this
with the Go runtime, which tried to do exactly this.