linux-kernel - Re: [patch V6 00/37] x86/entry: Rework leftovers and merge plan

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Date:   Mon, 18 May 2020 18:07:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        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>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>
Subject: Re: [patch V6 00/37] x86/entry: Rework leftovers and merge plan


So on top of you entry-v8-full; I had to chase one of those
instrumentation_end() escapes an (extended) basic block chase (again!).

How about we do something like the below; that fixes the current case
(rcu_eqs_enter) but also kills the entire class.

---
 arch/x86/include/asm/bug.h     |  2 +-
 include/linux/compiler.h       | 16 +++++++++++++---
 include/linux/compiler_types.h |  4 ----
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index f128e5c2ed42..fb34ff641e0a 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -79,8 +79,8 @@ do {								\
 do {								\
 	instrumentation_begin();				\
 	_BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));		\
-	instrumentation_end();					\
 	annotate_reachable();					\
+	instrumentation_end();					\
 } while (0)
 
 #include <asm-generic/bug.h>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7db5902f8f6e..b4c248e6b76a 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -120,25 +120,35 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 /* Annotate a C jump table to allow objtool to follow the code flow */
 #define __annotate_jump_table __section(.rodata..c_jump_table)
 
+#ifdef CONFIG_DEBUG_ENTRY
+/* Section for code which can't be instrumented at all */
+#define noinstr								\
+	noinline notrace __attribute((__section__(".noinstr.text")))
+
 /* Begin/end of an instrumentation safe region */
-#define instrumentation_begin() ({						\
+#define instrumentation_begin() ({					\
 	asm volatile("%c0:\n\t"						\
 		     ".pushsection .discard.instr_begin\n\t"		\
 		     ".long %c0b - .\n\t"				\
 		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
 
-#define instrumentation_end() ({							\
-	asm volatile("%c0:\n\t"						\
+#define instrumentation_end() ({					\
+	asm volatile("%c0: nop\n\t"					\
 		     ".pushsection .discard.instr_end\n\t"		\
 		     ".long %c0b - .\n\t"				\
 		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
+#endif /* CONFIG_DEBUG_ENTRY */
 
 #else
 #define annotate_reachable()
 #define annotate_unreachable()
 #define __annotate_jump_table
+#endif
+
+#ifndef noinstr
+#define noinstr noinline notrace
 #define instrumentation_begin()		do { } while(0)
 #define instrumentation_end()		do { } while(0)
 #endif
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index ea15ea99efb4..6ed0612bc143 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -118,10 +118,6 @@ struct ftrace_likely_data {
 #define notrace			__attribute__((__no_instrument_function__))
 #endif
 
-/* Section for code which can't be instrumented at all */
-#define noinstr								\
-	noinline notrace __attribute((__section__(".noinstr.text")))
-
 /*
  * it doesn't make sense on ARM (currently the only user of __naked)
  * to trace naked functions because then mcount is called without