From: Andrew Cooper <andrew.cooper3@citrix.com>
To: <peterz@infradead.org>, Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Kyle Huey <me@kylehuey.com>,
Alexandre Chartre <alexandre.chartre@oracle.com>,
"Robert O'Callahan" <rocallahan@gmail.com>,
"Paul E. McKenney" <paulmck@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>,
"Josh Poimboeuf" <jpoimboe@redhat.com>,
Daniel Thompson <daniel.thompson@linaro.org>
Subject: Re: [PATCH v2 5/8] x86/debug: Simplify #DB signal code
Date: Mon, 24 Aug 2020 12:26:01 +0100 [thread overview]
Message-ID: <b5ff8a44-1039-645c-de3e-d5f085cbc3f0@citrix.com> (raw)
In-Reply-To: <20200824110501.GT1362448@hirez.programming.kicks-ass.net>
On 24/08/2020 12:05, peterz@infradead.org wrote:
> On Sun, Aug 23, 2020 at 04:09:42PM -0700, Andy Lutomirski wrote:
>> On Fri, Aug 21, 2020 at 3:21 AM Peter Zijlstra <peterz@infradead.org> wrote:
>>> Get rid of the two variables, avoid computing si_code when not needed
>>> and be consistent about which dr6 value is used.
>>>
>>> - if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
>>> - send_sigtrap(regs, 0, si_code);
>>> + /*
>>> + * If dr6 has no reason to give us about the origin of this trap,
>>> + * then it's very likely the result of an icebp/int01 trap.
>>> + * User wants a sigtrap for that.
>>> + */
>>> + if (dr6 & (DR_STEP | DR_TRAP_BITS) || !dr6)
>>> + send_sigtrap(regs, 0, get_si_code(dr6));
>> The old condition was ... || (actual DR6 value) and the new condition
>> was ... || (stupid notifier-modified DR6 value). I think the old code
>> was more correct.
> Hurmph.. /me goes re-read the SDM.
>
> 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
Traps on previous instructions are at priority 4, because they still
"part" of the previous instruction. X breakpoints are priority 7.
The two #DB's shouldn't merge because nothing inhibits delivery[1] of
the trap at priority 4, and on return from the handler, RF isn't set so
the instruction breakpoint will trigger.
~Andrew
[1] Anyone playing with MovSS gets to keep all resulting pieces.
next prev parent reply other threads:[~2020-08-24 11:26 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 9:39 [PATCH v2 0/8] x86/debug: Untangle handle_debug() Peter Zijlstra
2020-08-21 9:39 ` [PATCH v2 1/8] x86/debug: Allow a single level of #DB recursion Peter Zijlstra
2020-08-21 9:39 ` [PATCH v2 2/8] x86/debug: Sync BTF earlier Peter Zijlstra
2020-08-23 23:03 ` Andy Lutomirski
2020-08-21 9:39 ` [PATCH v2 3/8] x86/debug: Move kprobe_debug_handler() into exc_debug_kernel() Peter Zijlstra
2020-08-23 23:01 ` Andy Lutomirski
2020-08-21 9:39 ` [PATCH v2 4/8] x86/debug: Remove handle_debug(.user) argument Peter Zijlstra
2020-08-23 23:05 ` Andy Lutomirski
2020-08-21 9:39 ` [PATCH v2 5/8] x86/debug: Simplify #DB signal code Peter Zijlstra
2020-08-23 23:09 ` Andy Lutomirski
2020-08-24 11:05 ` peterz
2020-08-24 11:26 ` Andrew Cooper [this message]
2020-08-24 12:00 ` peterz
2020-08-24 23:07 ` Andy Lutomirski
2020-08-24 23:09 ` Andy Lutomirski
2020-08-21 9:39 ` [PATCH v2 6/8] x86/debug: Move historical SYSENTER junk into exc_debug_kernel() Peter Zijlstra
2020-08-21 9:39 ` [PATCH v2 7/8] x86/debug: Move cond_local_irq_enable() block into exc_debug_user() Peter Zijlstra
2020-08-21 9:39 ` [PATCH v2 8/8] x86/debug: Remove the historical junk Peter Zijlstra
2020-08-21 12:22 ` [PATCH v2.1 " peterz
2020-08-23 23:11 ` [PATCH v2 " Andy Lutomirski
2020-08-21 12:56 ` [PATCH v2 0/8] x86/debug: Untangle handle_debug() peterz
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