[PATCH v5 07/17] static_call: Add inline static call infrastructure

Peter Zijlstra
2020-06-24T15:52:57Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

Add infrastructure for an arch-specific CONFIG_HAVE_STATIC_CALL_INLINE
option, which is a faster version of CONFIG_HAVE_STATIC_CALL. At
runtime, the static call sites are patched directly, rather than using
the out-of-line trampolines.

Compared to out-of-line static calls, the performance benefits are more
modest, but still measurable. Steven Rostedt did some tracepoint
measurements:

https://lkml.kernel.org/r/20181126155405.72b4f718@gandalf.local.home

This code is heavily inspired by the jump label code (aka "static
jumps"), as some of the concepts are very similar.

For more details, see the comments in include/linux/static_call.h.

[peterz: simplified interface; merged trampolines]
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/Kconfig | 4
include/asm-generic/vmlinux.lds.h | 7
include/linux/module.h | 5
include/linux/static_call.h | 36 ++++
include/linux/static_call_types.h | 13 +
kernel/Makefile | 1
kernel/module.c | 5
kernel/static_call.c | 303 ++++++++++++++++++++++++++++++++++++++
8 files changed, 373 insertions(+), 1 deletion(-)
create mode 100644 kernel/static_call.c

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -982,6 +982,10 @@ config HAVE_SPARSE_SYSCALL_NR
config HAVE_STATIC_CALL
bool

+config HAVE_STATIC_CALL_INLINE
+ bool
+ depends on HAVE_STATIC_CALL
+
source "kernel/gcov/Kconfig"

source "scripts/gcc-plugins/Kconfig"
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -368,6 +368,12 @@
KEEP(*(__jump_table)) \
__stop___jump_table = .;

+#define STATIC_CALL_DATA \
+ . = ALIGN(8); \
+ __start_static_call_sites = .; \
+ KEEP(*(.static_call_sites)) \
+ __stop_static_call_sites = .;
+
/*
* Allow architectures to handle ro_after_init data on their
* own by defining an empty RO_AFTER_INIT_DATA.
@@ -377,6 +383,7 @@
__start_ro_after_init = .; \
*(.data..ro_after_init) \
JUMP_TABLE_DATA \
+ STATIC_CALL_DATA \
__end_ro_after_init = .;
#endif

--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -25,6 +25,7 @@
#include <linux/error-injection.h>
#include <linux/tracepoint-defs.h>
#include <linux/srcu.h>
+#include <linux/static_call_types.h>

#include <linux/percpu.h>
#include <asm/module.h>
@@ -497,6 +498,10 @@ struct module {
unsigned long *kprobe_blacklist;
unsigned int num_kprobe_blacklist;
#endif
+#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
+ int num_static_call_sites;
+ struct static_call_site *static_call_sites;
+#endif

#ifdef CONFIG_LIVEPATCH
bool klp; /* Is this a livepatch module? */
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -95,7 +95,41 @@ extern void arch_static_call_transform(v
STATIC_CALL_TRAMP_ADDR(name), func); \
})

-#if defined(CONFIG_HAVE_STATIC_CALL)
+#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
+
+struct static_call_mod {
+ struct static_call_mod *next;
+ struct module *mod; /* for vmlinux, mod == NULL */
+ struct static_call_site *sites;
+};
+
+struct static_call_key {
+ void *func;
+ struct static_call_mod *mods;
+};
+
+extern void __static_call_update(struct static_call_key *key, void *tramp, void *func);
+extern int static_call_mod_init(struct module *mod);
+
+#define DEFINE_STATIC_CALL(name, _func) \
+ DECLARE_STATIC_CALL(name, _func); \
+ struct static_call_key STATIC_CALL_KEY(name) = { \
+ .func = _func, \
+ .mods = NULL, \
+ }; \
+ ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+
+#define static_call(name) __static_call(name)
+
+#define EXPORT_STATIC_CALL(name) \
+ EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
+ EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
+
+#define EXPORT_STATIC_CALL_GPL(name) \
+ EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \
+ EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
+
+#elif defined(CONFIG_HAVE_STATIC_CALL)

struct static_call_key {
void *func;
--- a/include/linux/static_call_types.h
+++ b/include/linux/static_call_types.h
@@ -2,14 +2,27 @@
#ifndef _STATIC_CALL_TYPES_H
#define _STATIC_CALL_TYPES_H

+#include <linux/types.h>
#include <linux/stringify.h>

#define STATIC_CALL_KEY_PREFIX __SCK__
+#define STATIC_CALL_KEY_PREFIX_STR __stringify(STATIC_CALL_KEY_PREFIX)
+#define STATIC_CALL_KEY_PREFIX_LEN (sizeof(STATIC_CALL_KEY_PREFIX_STR) - 1)
#define STATIC_CALL_KEY(name) __PASTE(STATIC_CALL_KEY_PREFIX, name)

#define STATIC_CALL_TRAMP_PREFIX __SCT__
#define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX)
+#define STATIC_CALL_TRAMP_PREFIX_LEN (sizeof(STATIC_CALL_TRAMP_PREFIX_STR) - 1)
#define STATIC_CALL_TRAMP(name) __PASTE(STATIC_CALL_TRAMP_PREFIX, name)
#define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name))

+/*
+ * The static call site table needs to be created by external tooling (objtool
+ * or a compiler plugin).
+ */
+struct static_call_site {
+ s32 addr;
+ s32 key;
+};
+
#endif /* _STATIC_CALL_TYPES_H */
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -109,6 +109,7 @@ obj-$(CONFIG_CPU_PM) += cpu_pm.o
obj-$(CONFIG_BPF) += bpf/
obj-$(CONFIG_KCSAN) += kcsan/
obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
+obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o

obj-$(CONFIG_PERF_EVENTS) += events/

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3226,6 +3226,11 @@ static int find_module_sections(struct m
sizeof(unsigned long),
&mod->num_kprobe_blacklist);
#endif
+#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
+ mod->static_call_sites = section_objs(info, ".static_call_sites",
+ sizeof(*mod->static_call_sites),
+ &mod->num_static_call_sites);
+#endif
mod->extable = section_objs(info, "__ex_table",
sizeof(*mod->extable), &mod->num_exentries);

--- /dev/null
+++ b/kernel/static_call.c
@@ -0,0 +1,303 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/init.h>
+#include <linux/static_call.h>
+#include <linux/bug.h>
+#include <linux/smp.h>
+#include <linux/sort.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/cpu.h>
+#include <linux/processor.h>
+#include <asm/sections.h>
+
+extern struct static_call_site __start_static_call_sites[],
+ __stop_static_call_sites[];
+
+static bool static_call_initialized;
+
+#define STATIC_CALL_INIT 1UL
+
+/* mutex to protect key modules/sites */
+static DEFINE_MUTEX(static_call_mutex);
+
+static void static_call_lock(void)
+{
+ mutex_lock(&static_call_mutex);
+}
+
+static void static_call_unlock(void)
+{
+ mutex_unlock(&static_call_mutex);
+}
+
+static inline void *static_call_addr(struct static_call_site *site)
+{
+ return (void *)((long)site->addr + (long)&site->addr);
+}
+
+
+static inline struct static_call_key *static_call_key(const struct static_call_site *site)
+{
+ return (struct static_call_key *)
+ (((long)site->key + (long)&site->key) & ~STATIC_CALL_INIT);
+}
+
+/* These assume the key is word-aligned. */
+static inline bool static_call_is_init(struct static_call_site *site)
+{
+ return ((long)site->key + (long)&site->key) & STATIC_CALL_INIT;
+}
+
+static inline void static_call_set_init(struct static_call_site *site)
+{
+ site->key = ((long)static_call_key(site) | STATIC_CALL_INIT) -
+ (long)&site->key;
+}
+
+static int static_call_site_cmp(const void *_a, const void *_b)
+{
+ const struct static_call_site *a = _a;
+ const struct static_call_site *b = _b;
+ const struct static_call_key *key_a = static_call_key(a);
+ const struct static_call_key *key_b = static_call_key(b);
+
+ if (key_a < key_b)
+ return -1;
+
+ if (key_a > key_b)
+ return 1;
+
+ return 0;
+}
+
+static void static_call_site_swap(void *_a, void *_b, int size)
+{
+ long delta = (unsigned long)_a - (unsigned long)_b;
+ struct static_call_site *a = _a;
+ struct static_call_site *b = _b;
+ struct static_call_site tmp = *a;
+
+ a->addr = b->addr - delta;
+ a->key = b->key - delta;
+
+ b->addr = tmp.addr + delta;
+ b->key = tmp.key + delta;
+}
+
+static inline void static_call_sort_entries(struct static_call_site *start,
+ struct static_call_site *stop)
+{
+ sort(start, stop - start, sizeof(struct static_call_site),
+ static_call_site_cmp, static_call_site_swap);
+}
+
+void __static_call_update(struct static_call_key *key, void *tramp, void *func)
+{
+ struct static_call_site *site, *stop;
+ struct static_call_mod *site_mod;
+
+ cpus_read_lock();
+ static_call_lock();
+
+ if (key->func == func)
+ goto done;
+
+ key->func = func;
+
+ arch_static_call_transform(NULL, tramp, func);
+
+ /*
+ * If uninitialized, we'll not update the callsites, but they still
+ * point to the trampoline and we just patched that.
+ */
+ if (WARN_ON_ONCE(!static_call_initialized))
+ goto done;
+
+ for (site_mod = key->mods; site_mod; site_mod = site_mod->next) {
+ struct module *mod = site_mod->mod;
+
+ if (!site_mod->sites) {
+ /*
+ * This can happen if the static call key is defined in
+ * a module which doesn't use it.
+ */
+ continue;
+ }
+
+ stop = __stop_static_call_sites;
+
+#ifdef CONFIG_MODULES
+ if (mod) {
+ stop = mod->static_call_sites +
+ mod->num_static_call_sites;
+ }
+#endif
+
+ for (site = site_mod->sites;
+ site < stop && static_call_key(site) == key; site++) {
+ void *site_addr = static_call_addr(site);
+
+ if (static_call_is_init(site)) {
+ /*
+ * Don't write to call sites which were in
+ * initmem and have since been freed.
+ */
+ if (!mod && system_state >= SYSTEM_RUNNING)
+ continue;
+ if (mod && !within_module_init((unsigned long)site_addr, mod))
+ continue;
+ }
+
+ if (!kernel_text_address((unsigned long)site_addr)) {
+ WARN_ONCE(1, "can't patch static call site at %pS",
+ site_addr);
+ continue;
+ }
+
+ arch_static_call_transform(site_addr, NULL, func);
+ }
+ }
+
+done:
+ static_call_unlock();
+ cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(__static_call_update);
+
+static int __static_call_init(struct module *mod,
+ struct static_call_site *start,
+ struct static_call_site *stop)
+{
+ struct static_call_site *site;
+ struct static_call_key *key, *prev_key = NULL;
+ struct static_call_mod *site_mod;
+
+ if (start == stop)
+ return 0;
+
+ static_call_sort_entries(start, stop);
+
+ for (site = start; site < stop; site++) {
+ void *site_addr = static_call_addr(site);
+
+ if ((mod && within_module_init((unsigned long)site_addr, mod)) ||
+ (!mod && init_section_contains(site_addr, 1)))
+ static_call_set_init(site);
+
+ key = static_call_key(site);
+ if (key != prev_key) {
+ prev_key = key;
+
+ site_mod = kzalloc(sizeof(*site_mod), GFP_KERNEL);
+ if (!site_mod)
+ return -ENOMEM;
+
+ site_mod->mod = mod;
+ site_mod->sites = site;
+ site_mod->next = key->mods;
+ key->mods = site_mod;
+ }
+
+ arch_static_call_transform(site_addr, NULL, key->func);
+ }
+
+ return 0;
+}
+
+#ifdef CONFIG_MODULES
+
+static int static_call_add_module(struct module *mod)
+{
+ return __static_call_init(mod, mod->static_call_sites,
+ mod->static_call_sites + mod->num_static_call_sites);
+}
+
+static void static_call_del_module(struct module *mod)
+{
+ struct static_call_site *start = mod->static_call_sites;
+ struct static_call_site *stop = mod->static_call_sites +
+ mod->num_static_call_sites;
+ struct static_call_key *key, *prev_key = NULL;
+ struct static_call_mod *site_mod, **prev;
+ struct static_call_site *site;
+
+ for (site = start; site < stop; site++) {
+ key = static_call_key(site);
+ if (key == prev_key)
+ continue;
+
+ prev_key = key;
+
+ for (prev = &key->mods, site_mod = key->mods;
+ site_mod && site_mod->mod != mod;
+ prev = &site_mod->next, site_mod = site_mod->next)
+ ;
+
+ if (!site_mod)
+ continue;
+
+ *prev = site_mod->next;
+ kfree(site_mod);
+ }
+}
+
+static int static_call_module_notify(struct notifier_block *nb,
+ unsigned long val, void *data)
+{
+ struct module *mod = data;
+ int ret = 0;
+
+ cpus_read_lock();
+ static_call_lock();
+
+ switch (val) {
+ case MODULE_STATE_COMING:
+ ret = static_call_add_module(mod);
+ if (ret) {
+ WARN(1, "Failed to allocate memory for static calls");
+ static_call_del_module(mod);
+ }
+ break;
+ case MODULE_STATE_GOING:
+ static_call_del_module(mod);
+ break;
+ }
+
+ static_call_unlock();
+ cpus_read_unlock();
+
+ return notifier_from_errno(ret);
+}
+
+static struct notifier_block static_call_module_nb = {
+ .notifier_call = static_call_module_notify,
+};
+
+#endif /* CONFIG_MODULES */
+
+static void __init static_call_init(void)
+{
+ int ret;
+
+ if (static_call_initialized)
+ return;
+
+ cpus_read_lock();
+ static_call_lock();
+ ret = __static_call_init(NULL, __start_static_call_sites,
+ __stop_static_call_sites);
+ static_call_unlock();
+ cpus_read_unlock();
+
+ if (ret) {
+ pr_err("Failed to allocate memory for static_call!\n");
+ BUG();
+ }
+
+ static_call_initialized = true;
+
+#ifdef CONFIG_MODULES
+ register_module_notifier(&static_call_module_nb);
+#endif
+}
+early_initcall(static_call_init);