linux-kernel - Re: [PATCH v2 5/8] x86/debug: Simplify #DB signal code

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Date:   Mon, 24 Aug 2020 14:00:17 +0200
From:   peterz@...radead.org
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     Andy Lutomirski <luto@...nel.org>, 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>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        Daniel Thompson <daniel.thompson@...aro.org>
Subject: Re: [PATCH v2 5/8] x86/debug: Simplify #DB signal code

On Mon, Aug 24, 2020 at 12:26:01PM +0100, Andrew Cooper wrote:

> > INT1 is a trap,
> > instruction breakpoint is a fault
> >
> > So if you have:
> >
> > 	INT1
> > 1:	some-instr
> >
> > and set an X breakpoint on 1, we'll loose the INT1, right?
> 
> You should get two.  First with a dr6 of 0 (ICEBP, RIP pointing at 1:),
> and a second with dr6 indicating the X breakpoint (again, RIP pointing
> at 1:).
> 
> SDM Vol3 6.9 PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS

Ooh, shiny. Clearly I didn't read enough SDM this morning.