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Message-ID: <20240313180106.2917308-2-vschneid@redhat.com>
Date: Wed, 13 Mar 2024 19:01:03 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: linux-kernel@...r.kernel.org,
kvm@...r.kernel.org,
linux-arch@...r.kernel.org,
x86@...nel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Arnd Bergmann <arnd@...db.de>,
Jason Baron <jbaron@...mai.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ard Biesheuvel <ardb@...nel.org>,
Frederic Weisbecker <frederic@...nel.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Feng Tang <feng.tang@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Mike Rapoport (IBM)" <rppt@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
David Hildenbrand <david@...hat.com>,
"ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
Michael Kelley <mikelley@...rosoft.com>,
"Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Subject: [PATCH v3 1/4] jump_label,module: Don't alloc static_key_mod for __ro_after_init keys
From: Peter Zijlstra <peterz@...radead.org>
When a static_key is marked ro_after_init, its state will never change
(after init), therefore jump_label_update() will never need to iterate
the entries, and thus module load won't actually need to track this --
avoiding the static_key::next write.
Therefore, mark these keys such that jump_label_add_module() might
recognise them and avoid the modification.
Use the special state: 'static_key_linked(key) && !static_key_mod(key)'
to denote such keys.
jump_label_add_module() does not exist under CONFIG_JUMP_LABEL=n, so the
newly-introduced jump_label_ro() can be defined as a nop for that
configuration.
Link: http://lore.kernel.org/r/20230705204142.GB2813335@hirez.programming.kicks-ass.net
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
[Added comments and build fix]
Signed-off-by: Valentin Schneider <vschneid@...hat.com>
Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
include/asm-generic/sections.h | 5 ++++
include/linux/jump_label.h | 3 ++
init/main.c | 1 +
kernel/jump_label.c | 53 ++++++++++++++++++++++++++++++++++
4 files changed, 62 insertions(+)
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index db13bb620f527..c768de6f19a9a 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -180,6 +180,11 @@ static inline bool is_kernel_rodata(unsigned long addr)
addr < (unsigned long)__end_rodata;
}
+static inline bool is_kernel_ro_after_init(unsigned long addr)
+{
+ return addr >= (unsigned long)__start_ro_after_init &&
+ addr < (unsigned long)__end_ro_after_init;
+}
/**
* is_kernel_inittext - checks if the pointer address is located in the
* .init.text section
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index f0a949b7c9733..3b103d88c139e 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -216,6 +216,7 @@ extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
extern void jump_label_init(void);
+extern void jump_label_ro(void);
extern void jump_label_lock(void);
extern void jump_label_unlock(void);
extern void arch_jump_label_transform(struct jump_entry *entry,
@@ -265,6 +266,8 @@ static __always_inline void jump_label_init(void)
static_key_initialized = true;
}
+static __always_inline void jump_label_ro(void) { }
+
static __always_inline bool static_key_false(struct static_key *key)
{
if (unlikely_notrace(static_key_count(key) > 0))
diff --git a/init/main.c b/init/main.c
index 7dce08198b133..6fc421b4d5fdb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1412,6 +1412,7 @@ static void mark_readonly(void)
* insecure pages which are W+X.
*/
rcu_barrier();
+ jump_label_ro();
mark_rodata_ro();
rodata_test();
} else
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index d9c822bbffb8d..7e3e8d1a0fea7 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -530,6 +530,45 @@ void __init jump_label_init(void)
cpus_read_unlock();
}
+static inline bool static_key_sealed(struct static_key *key)
+{
+ return (key->type & JUMP_TYPE_LINKED) && !(key->type & ~JUMP_TYPE_MASK);
+}
+
+static inline void static_key_seal(struct static_key *key)
+{
+ unsigned long type = key->type & JUMP_TYPE_TRUE;
+ key->type = JUMP_TYPE_LINKED | type;
+}
+
+void jump_label_ro(void)
+{
+ struct jump_entry *iter_start = __start___jump_table;
+ struct jump_entry *iter_stop = __stop___jump_table;
+ struct jump_entry *iter;
+
+ if (WARN_ON_ONCE(!static_key_initialized))
+ return;
+
+ cpus_read_lock();
+ jump_label_lock();
+
+ for (iter = iter_start; iter < iter_stop; iter++) {
+ struct static_key *iterk = jump_entry_key(iter);
+
+ if (!is_kernel_ro_after_init((unsigned long)iterk))
+ continue;
+
+ if (static_key_sealed(iterk))
+ continue;
+
+ static_key_seal(iterk);
+ }
+
+ jump_label_unlock();
+ cpus_read_unlock();
+}
+
#ifdef CONFIG_MODULES
enum jump_label_type jump_label_init_type(struct jump_entry *entry)
@@ -650,6 +689,15 @@ static int jump_label_add_module(struct module *mod)
static_key_set_entries(key, iter);
continue;
}
+
+ /*
+ * If the key was sealed at init, then there's no need to keep a
+ * reference to its module entries - just patch them now and be
+ * done with it.
+ */
+ if (static_key_sealed(key))
+ goto do_poke;
+
jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
if (!jlm)
return -ENOMEM;
@@ -675,6 +723,7 @@ static int jump_label_add_module(struct module *mod)
static_key_set_linked(key);
/* Only update if we've changed from our initial state */
+do_poke:
if (jump_label_type(iter) != jump_label_init_type(iter))
__jump_label_update(key, iter, iter_stop, true);
}
@@ -699,6 +748,10 @@ static void jump_label_del_module(struct module *mod)
if (within_module((unsigned long)key, mod))
continue;
+ /* No @jlm allocated because key was sealed at init. */
+ if (static_key_sealed(key))
+ continue;
+
/* No memory during module load */
if (WARN_ON(!static_key_linked(key)))
continue;
--
2.43.0
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