[PATCH V5 7/7] x86/jump_label: Batch jump label updates

[Daniel Bristot de Oliveira]

Currently, the jump label of a static key is transformed via the arch
specific function:

    void arch_jump_label_transform(struct jump_entry *entry,
                                   enum jump_label_type type)

The new approach (batch mode) uses two arch functions, the first has the
same arguments of the arch_jump_label_transform(), and is the function:

  int arch_jump_label_transform_queue(struct jump_entry *entry,
                                      enum jump_label_type type)

Rather than transforming the code, it adds the jump_entry in a queue of
entries to be updated. This functions returns 0 in the case of a
successful enqueue of an entry. If it returns !0, the caller must to
apply the queue and then try to queue again, for instance, because the
queue is full.

This function expects the caller to sort the entries by the address before
enqueueuing then. This is already done by the arch independent code, though.

After queuing all jump_entries, the function:

    void arch_jump_label_transform_apply(void)

Applies the changes in the queue.

Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Scott Wood <swood@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Clark Williams <williams@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/include/asm/jump_label.h |  2 +
 arch/x86/kernel/jump_label.c      | 88 +++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 65191ce8e1cf..06c3cc22a058 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -2,6 +2,8 @@
 #ifndef _ASM_X86_JUMP_LABEL_H
 #define _ASM_X86_JUMP_LABEL_H
 
+#define HAVE_JUMP_LABEL_BATCH
+
 #define JUMP_LABEL_NOP_SIZE 5
 
 #ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 8aa65fbbd764..ab75b222a7e2 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -15,6 +15,7 @@
 #include <asm/kprobes.h>
 #include <asm/alternative.h>
 #include <asm/text-patching.h>
+#include <linux/slab.h>
 
 union jump_code_union {
 	char code[JUMP_LABEL_NOP_SIZE];
@@ -111,6 +112,93 @@ void arch_jump_label_transform(struct jump_entry *entry,
 	mutex_unlock(&text_mutex);
 }
 
+unsigned int entry_vector_max_elem __read_mostly;
+struct text_patch_loc *entry_vector;
+unsigned int entry_vector_nr_elem;
+
+void arch_jump_label_init(void)
+{
+	entry_vector = (void *) __get_free_page(GFP_KERNEL);
+
+	if (WARN_ON_ONCE(!entry_vector))
+		return;
+
+	entry_vector_max_elem = PAGE_SIZE / sizeof(struct text_patch_loc);
+	return;
+}
+
+int arch_jump_label_transform_queue(struct jump_entry *entry,
+				     enum jump_label_type type)
+{
+	struct text_patch_loc *tp;
+	void *entry_code;
+
+	/*
+	 * Batch mode disabled before being able to allocate memory:
+	 * Fallback to the non-batching mode.
+	 */
+	if (unlikely(!entry_vector_max_elem)) {
+		if (!slab_is_available() || early_boot_irqs_disabled)
+			goto fallback;
+
+		arch_jump_label_init();
+	}
+
+	/*
+	 * No more space in the vector, tell upper layer to apply
+	 * the queue before continuing.
+	 */
+	if (entry_vector_nr_elem == entry_vector_max_elem)
+		return -ENOSPC;
+
+	tp = &entry_vector[entry_vector_nr_elem];
+
+	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 (entry_vector_nr_elem > 0) {
+		int prev_idx = entry_vector_nr_elem - 1;
+		struct text_patch_loc *prev_tp = &entry_vector[prev_idx];
+
+		if (WARN_ON_ONCE(prev_tp->addr > entry_code))
+			return -EINVAL;
+	}
+
+	__jump_label_set_jump_code(entry, type,
+				   (union jump_code_union *) &tp->opcode, 0);
+
+	tp->addr = entry_code;
+	tp->detour = entry_code + JUMP_LABEL_NOP_SIZE;
+	tp->len = JUMP_LABEL_NOP_SIZE;
+
+	entry_vector_nr_elem++;
+
+	return 0;
+
+fallback:
+	arch_jump_label_transform(entry, type);
+	return 0;
+}
+
+void arch_jump_label_transform_apply(void)
+{
+	if (early_boot_irqs_disabled || !entry_vector_nr_elem)
+		return;
+
+	mutex_lock(&text_mutex);
+	text_poke_bp_batch(entry_vector, entry_vector_nr_elem);
+	mutex_unlock(&text_mutex);
+
+	entry_vector_nr_elem = 0;
+}
+
 static enum {
 	JL_STATE_START,
 	JL_STATE_NO_UPDATE,
-- 
2.20.1