From: Peter Zijlstra <peterz@infradead.org>
To: x86@kernel.org
Cc: 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>,
Andy Lutomirski <luto@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Daniel Thompson <daniel.thompson@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>
Subject: [PATCH 09/13] x86/debug: Remove the historical junk
Date: Wed, 02 Sep 2020 15:25:58 +0200 [thread overview]
Message-ID: <20200902133201.170216274@infradead.org> (raw)
In-Reply-To: 20200902132549.496605622@infradead.org
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.
Suggested-by: Brian Gerst <brgerst@gmail.com>
Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/traps.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -843,18 +843,19 @@ static __always_inline void exc_debug_ke
if (notify_debug(regs, &dr6))
goto out;
- if (WARN_ON_ONCE(dr6 & DR_STEP)) {
- /*
- * Historical junk that used to handle SYSENTER single-stepping.
- * This should be unreachable now. If we survive for a while
- * without anyone hitting this warning, we'll turn this into
- * an oops.
- */
- dr6 &= ~DR_STEP;
- set_thread_flag(TIF_SINGLESTEP);
+ /*
+ * The kernel doesn't use TF single-step outside of:
+ *
+ * - Kprobes, consumed through kprobe_debug_handler()
+ * - KGDB, consumed through notify_debug()
+ *
+ * So if we get here with DR_STEP set, something is wonky.
+ *
+ * A known way to trigger this is through QEMU's GDB stub,
+ * which leaks #DB into the guest and causes IST recursion.
+ */
+ if (WARN_ON_ONCE(current->thread.debugreg6 & DR_STEP))
regs->flags &= ~X86_EFLAGS_TF;
- }
-
out:
instrumentation_end();
idtentry_exit_nmi(regs, irq_state);
next prev parent reply other threads:[~2020-09-02 15:46 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 13:25 [PATCH 00/13] x86/debug: Untangle handle_debug() Peter Zijlstra
2020-09-02 13:25 ` [PATCH 01/13] x86/entry: Fix AC assertion Peter Zijlstra
2020-09-02 15:58 ` Brian Gerst
2020-09-02 16:24 ` Jürgen Groß
2020-09-02 16:31 ` peterz
2020-09-02 17:02 ` Brian Gerst
2020-09-02 16:26 ` Andrew Cooper
2020-09-04 13:16 ` [tip: x86/urgent] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 02/13] x86/debug: Allow a single level of #DB recursion Peter Zijlstra
2020-09-02 23:59 ` Sasha Levin
2020-09-03 16:12 ` Josh Poimboeuf
2020-09-02 13:25 ` [PATCH 03/13] x86/debug: Sync BTF earlier Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 04/13] x86/debug: Move kprobe_debug_handler() into exc_debug_kernel() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 05/13] x86/debug: Remove handle_debug(.user) argument Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 06/13] x86/debug: Simplify #DB signal code Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 07/13] x86/debug: Move historical SYSENTER junk into exc_debug_kernel() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 08/13] x86/debug: Move cond_local_irq_enable() block into exc_debug_user() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` Peter Zijlstra [this message]
2020-09-04 13:16 ` [tip: x86/entry] x86/debug: Remove the historical junk tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 10/13] x86/debug: Remove aout_dump_debugregs() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [PATCH 11/13] x86/debug: Simplify hw_breakpoint_handler() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [RFC][PATCH 12/13] x86/debug: Support negative polarity DR6 bits Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [RFC][PATCH 13/13] x86/debug: Change thread.debugreg6 to thread.virtual_dr6 Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-03 15:21 ` [PATCH 00/13] x86/debug: Untangle handle_debug() Daniel Thompson
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