Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 4 15/24] x86/db: Split out dr6/7 handling
In-Reply-To: <20200508085909.GU5298@hirez.programming.kicks-ass.net>
References: <20200505134926.578885807@linutronix.de> <20200505135314.808628211@linutronix.de> <16c57a7e-8d39-d77e-915d-41b7f5e042fd@oracle.com> <20200508085909.GU5298@hirez.programming.kicks-ass.net>
Date:   Fri, 08 May 2020 13:58:30 +0200
Message-ID: <87wo5mk595.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Peter Zijlstra <peterz@infradead.org> writes:
>> > +static __always_inline void debug_enter(unsigned long *dr6, unsigned long *dr7)
>> > +{
>> > +	/*
>> > +	 * Disable breakpoints during exception handling; recursive exceptions
>> > +	 * are exceedingly 'fun'.
>> > +	 *
>> > +	 * Since this function is NOKPROBE, and that also applies to
>> > +	 * HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a
>> > +	 * HW_BREAKPOINT_W on our stack)
>> > +	 *
>> > +	 * Entry text is excluded for HW_BP_X and cpu_entry_area, which
>> > +	 * includes the entry stack is excluded for everything.
>> > +	 */
>> > +	get_debugreg(*dr7, 6);
>> 
>> Do you mean  get_debugreg(*dr7, 7); ?
>
> Shees, I have to go buy a new stack of brown paper bags at this rate,
> don't I :/

Not only you, but it's also  amazing that the selftests didn't catch
that.