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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Mon, 1 Aug 2022 21:40:48 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel <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 <linux-api@vger.kernel.org>,
        Peter Oskolkov <posk@posk.io>,
        Florian Weimer <fweimer@redhat.com>,
        Carlos O'Donell <carlos@redhat.com>
Subject: Re: [PATCH 2/2] rseq: Kill process when unknown flags are
 encountered in ABI structures
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* Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> The projects I know about that use rseq at the moment don't rely on the 
> old ABI ignoring unset flags:
> 
> - glibc initialize the rseq_abi()->flags to 0 and do not use rseq_abi()->rseq_cs->flags yet.
> - tcmalloc initialize rseq_abi()->flags and rseq_abi()->rseq_cs->flags to 0.
> - librseq (still only a master branch, no officially released public API yet) initialize
>   rseq_abi()->flags and rseq_abi()->rseq_cs->cs_flags to 0.
> - the Linux kernel selftests initialize rseq_abi()->flags and rseq_abi()->rseq_cs->cs_flags
>   to 0.
> - AFAIK DynamoRIO does not rely on the kernel ignoring unset flags bits.
> - AFAIK CRIU does not rely on the kernel ignoring unset flags bits.

Thanks - that's exhaustive enough.

> If anyone else rely on rseq ignoring those unset flags, please yell now.

Well, people are unlikely to see random lkml mails - but if gets reported 
as a regression then we need to revert. But I don't expect it to happen.

Thanks,

	Ingo