[RFC][ PATCH -tip v2 2/7] kprobes: introducing generic insn_slot framework

Masami Hiramatsu
2009-06-22T21:21:49Z

Make insn_slot framework support various size slots.
Current insn_slot just supports one-size instruction buffer slot. However,
kprobes jump optimization needs larger size buffers.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Anders Kaseorg <andersk@ksplice.com>
Cc: Tim Abbott <tabbott@ksplice.com>
---

kernel/kprobes.c | 96 +++++++++++++++++++++++++++++++++---------------------
1 files changed, 58 insertions(+), 38 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 0b68fdc..bc9cfd0 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -100,26 +100,38 @@ static struct kprobe_blackpoint kprobe_blacklist[] = {
* stepping on the instruction on a vmalloced/kmalloced/data page
* is a recipe for disaster
*/
-#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
-
struct kprobe_insn_page {
struct list_head list;
kprobe_opcode_t *insns; /* Page of instruction slots */
- char slot_used[INSNS_PER_PAGE];
int nused;
int ngarbage;
+ char slot_used[1];
+};
+
+struct kprobe_insn_cache {
+ struct list_head pages; /* list of kprobe_insn_page */
+ size_t insn_size; /* size of instruction slot */
+ int nr_garbage;
};

+static int slots_per_page(struct kprobe_insn_cache *c)
+{
+ return PAGE_SIZE/(c->insn_size * sizeof(kprobe_opcode_t));
+}
+
enum kprobe_slot_state {
SLOT_CLEAN = 0,
SLOT_DIRTY = 1,
SLOT_USED = 2,
};

-static DEFINE_MUTEX(kprobe_insn_mutex); /* Protects kprobe_insn_pages */
-static LIST_HEAD(kprobe_insn_pages);
-static int kprobe_garbage_slots;
-static int collect_garbage_slots(void);
+static DEFINE_MUTEX(kprobe_insn_mutex); /* Protects kprobe_insn_slots */
+static struct kprobe_insn_cache kprobe_insn_slots = {
+ .pages = LIST_HEAD_INIT(kprobe_insn_slots.pages),
+ .insn_size = MAX_INSN_SIZE,
+ .nr_garbage = 0,
+};
+static int __kprobes collect_garbage_slots(struct kprobe_insn_cache *c);

static int __kprobes check_safety(void)
{
@@ -149,32 +161,33 @@ loop_end:
* __get_insn_slot() - Find a slot on an executable page for an instruction.
* We allocate an executable page if there's no room on existing ones.
*/
-static kprobe_opcode_t __kprobes *__get_insn_slot(void)
+static kprobe_opcode_t __kprobes *__get_insn_slot(struct kprobe_insn_cache *c)
{
struct kprobe_insn_page *kip;

retry:
- list_for_each_entry(kip, &kprobe_insn_pages, list) {
- if (kip->nused < INSNS_PER_PAGE) {
+ list_for_each_entry(kip, &c->pages, list) {
+ if (kip->nused < slots_per_page(c)) {
int i;
- for (i = 0; i < INSNS_PER_PAGE; i++) {
+ for (i = 0; i < slots_per_page(c); i++) {
if (kip->slot_used[i] == SLOT_CLEAN) {
kip->slot_used[i] = SLOT_USED;
kip->nused++;
- return kip->insns + (i * MAX_INSN_SIZE);
+ return kip->insns + (i * c->insn_size);
}
}
- /* Surprise! No unused slots. Fix kip->nused. */
- kip->nused = INSNS_PER_PAGE;
+ /* kip->nused is broken. */
+ BUG();
}
}

/* If there are any garbage slots, collect it and try again. */
- if (kprobe_garbage_slots && collect_garbage_slots() == 0) {
+ if (c->nr_garbage && collect_garbage_slots(c) == 0)
goto retry;
- }
+
/* All out of space. Need to allocate a new page. Use slot 0. */
- kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
+ kip = kmalloc(sizeof(struct kprobe_insn_page) + slots_per_page(c) - 1,
+ GFP_KERNEL);
if (!kip)
return NULL;

@@ -189,19 +202,20 @@ static kprobe_opcode_t __kprobes *__get_insn_slot(void)
return NULL;
}
INIT_LIST_HEAD(&kip->list);
- list_add(&kip->list, &kprobe_insn_pages);
- memset(kip->slot_used, SLOT_CLEAN, INSNS_PER_PAGE);
+ memset(kip->slot_used, SLOT_CLEAN, slots_per_page(c));
kip->slot_used[0] = SLOT_USED;
kip->nused = 1;
kip->ngarbage = 0;
+ list_add(&kip->list, &c->pages);
return kip->insns;
}

+
kprobe_opcode_t __kprobes *get_insn_slot(void)
{
- kprobe_opcode_t *ret;
+ kprobe_opcode_t *ret = NULL;
mutex_lock(&kprobe_insn_mutex);
- ret = __get_insn_slot();
+ ret = __get_insn_slot(&kprobe_insn_slots);
mutex_unlock(&kprobe_insn_mutex);
return ret;
}
@@ -218,7 +232,7 @@ static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
* so as not to have to set it up again the
* next time somebody inserts a probe.
*/
- if (!list_is_singular(&kprobe_insn_pages)) {
+ if (!list_is_singular(&kip->list)) {
list_del(&kip->list);
module_free(NULL, kip->insns);
kfree(kip);
@@ -228,7 +242,7 @@ static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
return 0;
}

-static int __kprobes collect_garbage_slots(void)
+static int __kprobes collect_garbage_slots(struct kprobe_insn_cache *c)
{
struct kprobe_insn_page *kip, *next;
int safety;
@@ -240,42 +254,48 @@ static int __kprobes collect_garbage_slots(void)
if (safety != 0)
return -EAGAIN;

- list_for_each_entry_safe(kip, next, &kprobe_insn_pages, list) {
+ list_for_each_entry_safe(kip, next, &c->pages, list) {
int i;
if (kip->ngarbage == 0)
continue;
kip->ngarbage = 0; /* we will collect all garbages */
- for (i = 0; i < INSNS_PER_PAGE; i++) {
+ for (i = 0; i < slots_per_page(c); i++) {
if (kip->slot_used[i] == SLOT_DIRTY &&
collect_one_slot(kip, i))
break;
}
}
- kprobe_garbage_slots = 0;
+ c->nr_garbage = 0;
return 0;
}

-void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
+static void __kprobes __free_insn_slot(struct kprobe_insn_cache *c,
+ kprobe_opcode_t *slot, int dirty)
{
struct kprobe_insn_page *kip;

- mutex_lock(&kprobe_insn_mutex);
- list_for_each_entry(kip, &kprobe_insn_pages, list) {
- if (kip->insns <= slot &&
- slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
- int i = (slot - kip->insns) / MAX_INSN_SIZE;
+ list_for_each_entry(kip, &c->pages, list) {
+ long idx = ((long)slot - (long)kip->insns) / c->insn_size;
+ if (idx >= 0 && idx < slots_per_page(c)) {
+ WARN_ON(kip->slot_used[idx] != SLOT_USED);
if (dirty) {
- kip->slot_used[i] = SLOT_DIRTY;
+ kip->slot_used[idx] = SLOT_DIRTY;
kip->ngarbage++;
+ if (++c->nr_garbage > slots_per_page(c))
+ collect_garbage_slots(c);
} else
- collect_one_slot(kip, i);
- break;
+ collect_one_slot(kip, idx);
+ return;
}
}
+ /* Could not free this slot. */
+ WARN_ON(1);
+}

- if (dirty && ++kprobe_garbage_slots > INSNS_PER_PAGE)
- collect_garbage_slots();
-
+void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
+{
+ mutex_lock(&kprobe_insn_mutex);
+ __free_insn_slot(&kprobe_insn_slots, slot, dirty);
mutex_unlock(&kprobe_insn_mutex);
}
#endif