linux-kernel - Re: [REGRESSION] x86/debug: After PTRACE_SINGLESTEP DR

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Date:   Tue, 27 Oct 2020 18:56:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Kyle Huey <me@...ehuey.com>,
        open list <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Robert O'Callahan <rocallahan@...il.com>,
        Alexandre Chartre <alexandre.chartre@...cle.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>,
        Joel Fernandes <joel@...lfernandes.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Daniel Thompson <daniel.thompson@...aro.org>
Subject: Re: [REGRESSION] x86/debug: After PTRACE_SINGLESTEP DR_STEP is no
 longer reported in dr6

On Tue, Oct 27, 2020 at 10:08:14AM +0100, Peter Zijlstra wrote:
> On Mon, Oct 26, 2020 at 04:30:32PM -0700, Andy Lutomirski wrote:
> > Is there any compelling reason not to just drop the condition and do:
> > 
> > current->thread.virtual_dr6 |= (dr6 & DR_STEP);
> > 
> > unconditionally?
> 
> Because why should it?

Because WINE does indeed rely on that. I'll go post a new version.