linux-kernel - Re: [patch V4 part 1 35/36] x86: Replace ist_enter() with nmi

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Message-ID: <CALCETrXfemPJrVx+Nfp7k_PvKGezSK46_+dL5oNNV3o5i1qWVw@mail.gmail.com>
Date:   Thu, 7 May 2020 11:04:34 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 1 35/36] x86: Replace ist_enter() with nmi_enter()

On Tue, May 5, 2020 at 7:14 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> From: Peter Zijlstra <peterz@...radead.org>
>
> A few exceptions (like #DB and #BP) can happen at any location in the code,
> this then means that tracers should treat events from these exceptions as
> NMI-like. The interrupted context could be holding locks with interrupts
> disabled for instance.
>
> Similarly, #MC is an actual NMI-like exception.

Is it permissible to send a signal from inside nmi_enter()?  I imagine
so, but I just want to make sure.

--Andy