x86/alternatives, jump_label: Provide better text_poke() batching interface

Adding another text_poke_bp_batch() user made me realize the interface
is all sorts of wrong. The text poke vector should be internal to the
implementation.

This then results in a trivial interface:

  text_poke_queue()  - which has the 'normal' text_poke_bp() interface
  text_poke_finish() - which takes no arguments and flushes any
                       pending text_poke()s.

Tested-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191111132457.646280715@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 34 insertions, 65 deletions

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index c1a8b9e71408..cf8c847c7b5d 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -35,18 +35,19 @@ static void bug_at(unsigned char *ip, int line)
 	BUG();
 }
 
-static void __jump_label_set_jump_code(struct jump_entry *entry,
-				       enum jump_label_type type,
-				       union jump_code_union *code,
-				       int init)
+static const void *
+__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
 {
+	static union jump_code_union code; /* relies on text_mutex */
 	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 	const void *expect;
 	int line;
 
-	code->jump = 0xe9;
-	code->offset = jump_entry_target(entry) -
+	lockdep_assert_held(&text_mutex);
+
+	code.jump = JMP32_INSN_OPCODE;
+	code.offset = jump_entry_target(entry) -
 		       (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
 	if (init) {
@@ -54,23 +55,23 @@ static void __jump_label_set_jump_code(struct jump_entry *entry,
 	} else if (type == JUMP_LABEL_JMP) {
 		expect = ideal_nop; line = __LINE__;
 	} else {
-		expect = code->code; line = __LINE__;
+		expect = code.code; line = __LINE__;
 	}
 
 	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
 		bug_at((void *)jump_entry_code(entry), line);
 
 	if (type == JUMP_LABEL_NOP)
-		memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE);
+		memcpy(&code, ideal_nop, JUMP_LABEL_NOP_SIZE);
+
+	return &code;
 }
 
-static void __ref __jump_label_transform(struct jump_entry *entry,
-					 enum jump_label_type type,
-					 int init)
+static void inline __jump_label_transform(struct jump_entry *entry,
+					  enum jump_label_type type,
+					  int init)
 {
-	union jump_code_union code;
-
-	__jump_label_set_jump_code(entry, type, &code, init);
+	const void *opcode = __jump_label_set_jump_code(entry, type, init);
 
 	/*
 	 * As long as only a single processor is running and the code is still
@@ -84,31 +85,33 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 	 * always nop being the 'currently valid' instruction
 	 */
 	if (init || system_state == SYSTEM_BOOTING) {
-		text_poke_early((void *)jump_entry_code(entry), &code,
+		text_poke_early((void *)jump_entry_code(entry), opcode,
 				JUMP_LABEL_NOP_SIZE);
 		return;
 	}
 
-	text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL);
+	text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL);
 }
 
-void arch_jump_label_transform(struct jump_entry *entry,
-			       enum jump_label_type type)
+static void __ref jump_label_transform(struct jump_entry *entry,
+				       enum jump_label_type type,
+				       int init)
 {
 	mutex_lock(&text_mutex);
-	__jump_label_transform(entry, type, 0);
+	__jump_label_transform(entry, type, init);
 	mutex_unlock(&text_mutex);
 }
 
-#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
-static struct text_poke_loc tp_vec[TP_VEC_MAX];
-static int tp_vec_nr;
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	jump_label_transform(entry, type, 0);
+}
 
 bool arch_jump_label_transform_queue(struct jump_entry *entry,
 				     enum jump_label_type type)
 {
-	struct text_poke_loc *tp;
-	void *entry_code;
+	const void *opcode;
 
 	if (system_state == SYSTEM_BOOTING) {
 		/*
@@ -118,53 +121,19 @@ bool arch_jump_label_transform_queue(struct jump_entry *entry,
 		return true;
 	}
 
-	/*
-	 * No more space in the vector, tell upper layer to apply
-	 * the queue before continuing.
-	 */
-	if (tp_vec_nr == TP_VEC_MAX)
-		return false;
-
-	tp = &tp_vec[tp_vec_nr];
-
-	entry_code = (void *)jump_entry_code(entry);
-
-	/*
-	 * The INT3 handler will do a bsearch in the queue, so we need entries
-	 * to be sorted. We can survive an unsorted list by rejecting the entry,
-	 * forcing the generic jump_label code to apply the queue. Warning once,
-	 * to raise the attention to the case of an unsorted entry that is
-	 * better not happen, because, in the worst case we will perform in the
-	 * same way as we do without batching - with some more overhead.
-	 */
-	if (tp_vec_nr > 0) {
-		int prev = tp_vec_nr - 1;
-		struct text_poke_loc *prev_tp = &tp_vec[prev];
-
-		if (WARN_ON_ONCE(prev_tp->addr > entry_code))
-			return false;
-	}
-
-	__jump_label_set_jump_code(entry, type,
-				   (union jump_code_union *)&tp->text, 0);
-
-	text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
-
-	tp_vec_nr++;
-
+	mutex_lock(&text_mutex);
+	opcode = __jump_label_set_jump_code(entry, type, 0);
+	text_poke_queue((void *)jump_entry_code(entry),
+			opcode, JUMP_LABEL_NOP_SIZE, NULL);
+	mutex_unlock(&text_mutex);
 	return true;
 }
 
 void arch_jump_label_transform_apply(void)
 {
-	if (!tp_vec_nr)
-		return;
-
 	mutex_lock(&text_mutex);
-	text_poke_bp_batch(tp_vec, tp_vec_nr);
+	text_poke_finish();
 	mutex_unlock(&text_mutex);
-
-	tp_vec_nr = 0;
 }
 
 static enum {
@@ -193,5 +162,5 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 			jlstate = JL_STATE_NO_UPDATE;
 	}
 	if (jlstate == JL_STATE_UPDATE)
-		__jump_label_transform(entry, type, 1);
+		jump_label_transform(entry, type, 1);
 }