linux-kernel - Re: [PATCH v2 8/8] x86/debug: Remove the historical junk

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Message-ID: <CALCETrWJhes7QVmqit1XU+ioq13Ly7A9QJ5s4grp3+Vq75vMxw@mail.gmail.com>
Date:   Sun, 23 Aug 2020 16:11:18 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Kyle Huey <me@...ehuey.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        "Robert O'Callahan" <rocallahan@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        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>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Daniel Thompson <daniel.thompson@...aro.org>
Subject: Re: [PATCH v2 8/8] x86/debug: Remove the historical junk

On Fri, Aug 21, 2020 at 3:21 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Remove the historical junk and replace it with a WARN and a comment.
>
> The problem is that even though the kernel only uses TF single-step in
> kprobes and KGDB, both of which consume the event before this,
> QEMU/KVM has bugs in this area that can trigger this state so we have
> to deal with it.

Almost acked by me.

If you make the change I suggested earlier, then the ->debugreg6
garbage can actually die.

--Andy