[PATCH v2 0/5] jump_label: Fix __ro_after_init keys for modules & annotate some keys

[PATCH v2 0/5] jump_label: Fix __ro_after_init keys for modules & annotate some keys

[Valentin Schneider]

Hi folks,

This series fixes __ro_after_init keys used in modules (courtesy of PeterZ) and
flags more keys as __ro_after_init. Further context for why I'm looking into
this here: http://lore.kernel.org/r/20230720163056.2564824-1-vschneid@redhat.com

Compile & boot tested for x86_64_defconfig and i386_defconfig.


@Peter, regarding making __use_tsc x86_32, I hit a few snags.

Currently, for the static key to be enabled, we (mostly) need:
o X86_FEATURE_TSC is in CPUID
o determine_cpu_tsc_frequencies passes

All X86_64 systems have a TSC, so the CPUID feature is a given there.

Calibrating the TSC can end up depending on different things:
o CPUID accepting 0x16 as eax input (cf. cpu_khz_from_cpuid())
o MSR_FSB_FREQ being available (cf. cpu_khz_from_msr())
o pit_hpet_ptimer_calibrate_cpu() doesn't mess up

I couldn't find any guarantees for X86_64 on having the processor frequency
information CPUID leaf, nor for the FSB_FREQ MSR (both tsc_msr_cpu_ids and
the SDM seem to point at only a handful of models).

pit_hpet_ptimer_calibrate_cpu() relies on having either HPET or the ACPI PM
timer, the latter being widely available, though X86_PM_TIMER can be
disabled via EXPERT.

The question here is: are there any guarantees that at least one of these
can be relied upon for x86_64?

And with all of that, there is still the "apicpmtimer" cmdline option which
currently invokes notsc_setup() on x86_64. The justification I found for it was
in 0c3749c41f5e ("[PATCH] x86_64: Calibrate APIC timer using PM timer"):

  """
  On some broken motherboards (at least one NForce3 based AMD64 laptop)
  the PIT timer runs at a incorrect frequency.  This patch adds a new
  option "apicpmtimer" that allows to use the APIC timer and calibrate it
  using the PMTimer.
  """

Revisions
=========

v1 -> v2
++++++++

- Collected tags (Josh, Sean)
- Fixed CONFIG_JUMP_LABEL=n compile fail (lkp)

Cheers,
Valentin

Peter Zijlstra (1):
  jump_label,module: Don't alloc static_key_mod for __ro_after_init keys

Valentin Schneider (4):
  context_tracking: Make context_tracking_key __ro_after_init
  x86/kvm: Make kvm_async_pf_enabled __ro_after_init
  x86/speculation: Make mds_user_clear __ro_after_init
  x86/tsc: Make __use_tsc __ro_after_init

 arch/x86/kernel/cpu/bugs.c     |  2 +-
 arch/x86/kernel/kvm.c          |  2 +-
 arch/x86/kernel/tsc.c          |  2 +-
 include/asm-generic/sections.h |  5 ++++
 include/linux/jump_label.h     |  3 +++
 init/main.c                    |  1 +
 kernel/context_tracking.c      |  2 +-
 kernel/jump_label.c            | 49 ++++++++++++++++++++++++++++++++++
 8 files changed, 62 insertions(+), 4 deletions(-)

--
2.43.0

[PATCH v2 1/5] jump_label,module: Don't alloc static_key_mod for __ro_after_init keys

[Valentin Schneider]

From: Peter Zijlstra <peterz@infradead.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@infradead.org>
[Added comments and build fix]
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 include/asm-generic/sections.h |  5 ++++
 include/linux/jump_label.h     |  3 +++
 init/main.c                    |  1 +
 kernel/jump_label.c            | 49 ++++++++++++++++++++++++++++++++++
 4 files changed, 58 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 e24b0780fdff7..5f51d8b910dc1 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1407,6 +1407,7 @@ 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..25a5ed1147841 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);
 	}
-- 
2.43.0

[PATCH v2 2/5] context_tracking: Make context_tracking_key __ro_after_init

[Valentin Schneider]

context_tracking_key is only ever enabled in __init ct_cpu_tracker_user(),
so mark it as __ro_after_init.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 kernel/context_tracking.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6ef0b35fc28c5..cc4f3a57f848c 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -432,7 +432,7 @@ static __always_inline void ct_kernel_enter(bool user, int offset) { }
 #define CREATE_TRACE_POINTS
 #include <trace/events/context_tracking.h>
 
-DEFINE_STATIC_KEY_FALSE(context_tracking_key);
+DEFINE_STATIC_KEY_FALSE_RO(context_tracking_key);
 EXPORT_SYMBOL_GPL(context_tracking_key);
 
 static noinstr bool context_tracking_recursion_enter(void)
-- 
2.43.0

Re: [PATCH v2 2/5] context_tracking: Make context_tracking_key __ro_after_init

[kernel test robot]

Hello,

kernel test robot noticed "WARNING:at_kernel/jump_label.c:#jump_label_del_module" on:

commit: b42c2f5e8e4d403b5891b566b015177c8f471858 ("[PATCH v2 2/5] context_tracking: Make context_tracking_key __ro_after_init")
url: https://github.com/intel-lab-lkp/linux/commits/Valentin-Schneider/jump_label-module-Don-t-alloc-static_key_mod-for-__ro_after_init-keys/20240207-014501
base: https://git.kernel.org/cgit/virt/kvm/kvm.git queue
patch link: https://lore.kernel.org/all/20240206173911.4131670-3-vschneid@redhat.com/
patch subject: [PATCH v2 2/5] context_tracking: Make context_tracking_key __ro_after_init

in testcase: ltp
version: ltp-x86_64-14c1f76-1_20230715
with following parameters:

	test: kernel_misc



compiler: gcc-12
test machine: 8 threads 1 sockets Intel(R) Core(TM) i7-3770K CPU @ 3.50GHz (Ivy Bridge) with 16G memory

(please refer to attached dmesg/kmsg for entire log/backtrace)



If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202402191313.3276317d-oliver.sang@intel.com


[  215.214621][ T3608] ------------[ cut here ]------------
[ 215.214849][ T3608] WARNING: CPU: 1 PID: 3608 at kernel/jump_label.c:764 jump_label_del_module (kernel/jump_label.c:764 (discriminator 1)) 
[  215.215123][ T3608] Modules linked in: rcutorture(-) torture netconsole btrfs blake2b_generic xor raid6_pq zstd_compress libcrc32c intel_rapl_msr intel_rapl_common x86_pkg_temp_thermal intel_powerclamp sd_mod t10_pi coretemp crc64_rocksoft_generic crc64_rocksoft kvm_intel crc64 sg ipmi_devintf i915 ipmi_msghandler kvm irqbypass crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel sha512_ssse3 drm_buddy rapl intel_gtt intel_cstate drm_display_helper mxm_wmi firewire_ohci ttm ahci firewire_core libahci drm_kms_helper intel_uncore crc_itu_t libata i2c_i801 video i2c_smbus lpc_ich wmi binfmt_misc fuse drm ip_tables
[  215.216369][ T3608] CPU: 1 PID: 3608 Comm: modprobe Not tainted 6.7.0-rc7-00234-gb42c2f5e8e4d #1
[  215.216637][ T3608] Hardware name:  /DZ77BH-55K, BIOS BHZ7710H.86A.0097.2012.1228.1346 12/28/2012
[ 215.216918][ T3608] RIP: 0010:jump_label_del_module (kernel/jump_label.c:764 (discriminator 1)) 
[ 215.217162][ T3608] Code: 03 75 35 83 e6 03 48 09 f0 4c 89 fe 48 c1 ee 03 80 3c 2e 00 0f 85 cf 01 00 00 49 89 45 08 e9 bf fe ff ff 0f 0b e9 6b ff ff ff <0f> 0b e9 64 ff ff ff 0f 0b e9 e2 fe ff ff 0f 0b eb c7 0f 0b e9 19
All code
========
   0:	03 75 35             	add    0x35(%rbp),%esi
   3:	83 e6 03             	and    $0x3,%esi
   6:	48 09 f0             	or     %rsi,%rax
   9:	4c 89 fe             	mov    %r15,%rsi
   c:	48 c1 ee 03          	shr    $0x3,%rsi
  10:	80 3c 2e 00          	cmpb   $0x0,(%rsi,%rbp,1)
  14:	0f 85 cf 01 00 00    	jne    0x1e9
  1a:	49 89 45 08          	mov    %rax,0x8(%r13)
  1e:	e9 bf fe ff ff       	jmpq   0xfffffffffffffee2
  23:	0f 0b                	ud2    
  25:	e9 6b ff ff ff       	jmpq   0xffffffffffffff95
  2a:*	0f 0b                	ud2    		<-- trapping instruction
  2c:	e9 64 ff ff ff       	jmpq   0xffffffffffffff95
  31:	0f 0b                	ud2    
  33:	e9 e2 fe ff ff       	jmpq   0xffffffffffffff1a
  38:	0f 0b                	ud2    
  3a:	eb c7                	jmp    0x3
  3c:	0f 0b                	ud2    
  3e:	e9                   	.byte 0xe9
  3f:	19                   	.byte 0x19

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2    
   2:	e9 64 ff ff ff       	jmpq   0xffffffffffffff6b
   7:	0f 0b                	ud2    
   9:	e9 e2 fe ff ff       	jmpq   0xfffffffffffffef0
   e:	0f 0b                	ud2    
  10:	eb c7                	jmp    0xffffffffffffffd9
  12:	0f 0b                	ud2    
  14:	e9                   	.byte 0xe9
  15:	19                   	.byte 0x19
[  215.217593][ T3608] RSP: 0018:ffffc9000159fd38 EFLAGS: 00010297
[  215.217877][ T3608] RAX: 1ffffffff089982f RBX: 0000000000000000 RCX: ffffffffc14dc060
[  215.218140][ T3608] RDX: ffffffffc1c6b580 RSI: 0000000000000002 RDI: ffffffffc14dc000
[  215.218409][ T3608] RBP: dffffc0000000000 R08: ffffffffc1c6b8b8 R09: fffff520002b3fa6
[  215.218636][ T3608] R10: ffffc9000159fd37 R11: 0000000000000001 R12: ffffffff844cc178
[  215.218935][ T3608] R13: ffffffff844cc170 R14: ffffffffc14dc008 R15: ffffffff844cc178
[  215.219166][ T3608] FS:  00007f5e44068580(0000) GS:ffff888348080000(0000) knlGS:0000000000000000
[  215.219459][ T3608] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  215.219717][ T3608] CR2: 00007fceb9a28008 CR3: 00000001a718e005 CR4: 00000000001706f0
[  215.219956][ T3608] Call Trace:
[  215.220126][ T3608]  <TASK>
[ 215.220307][ T3608] ? __warn (kernel/panic.c:677) 
[ 215.220503][ T3608] ? jump_label_del_module (kernel/jump_label.c:764 (discriminator 1)) 
[ 215.220745][ T3608] ? report_bug (lib/bug.c:180 lib/bug.c:219) 
[ 215.220961][ T3608] ? handle_bug (arch/x86/kernel/traps.c:237) 
[ 215.221126][ T3608] ? exc_invalid_op (arch/x86/kernel/traps.c:258 (discriminator 1)) 
[ 215.221288][ T3608] ? asm_exc_invalid_op (arch/x86/include/asm/idtentry.h:568) 
[ 215.221543][ T3608] ? jump_label_del_module (kernel/jump_label.c:764 (discriminator 1)) 
[ 215.221835][ T3608] ? jump_label_add_module (kernel/jump_label.c:787) 
[ 215.222061][ T3608] jump_label_module_notify (kernel/jump_label.c:32 kernel/jump_label.c:807) 
[ 215.222255][ T3608] notifier_call_chain (kernel/notifier.c:95) 
[ 215.222433][ T3608] ? mutex_unlock (arch/x86/include/asm/atomic64_64.h:109 include/linux/atomic/atomic-arch-fallback.h:4308 include/linux/atomic/atomic-long.h:1499 include/linux/atomic/atomic-instrumented.h:4446 kernel/locking/mutex.c:181 kernel/locking/mutex.c:540) 
[ 215.222603][ T3608] blocking_notifier_call_chain (kernel/notifier.c:389 kernel/notifier.c:376) 
[ 215.222845][ T3608] __do_sys_delete_module+0x32a/0x540 
[ 215.223066][ T3608] ? module_flags (kernel/module/main.c:698) 
[ 215.223239][ T3608] ? __x64_sys_close (fs/open.c:1590 fs/open.c:1572 fs/open.c:1572) 
[ 215.223526][ T3608] ? kmem_cache_free (mm/slub.c:1826 mm/slub.c:3809 mm/slub.c:3831) 
[ 215.223772][ T3608] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83) 
[ 215.224010][ T3608] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129) 
[  215.224246][ T3608] RIP: 0033:0x7f5e44177847
[ 215.224423][ T3608] Code: 73 01 c3 48 8b 0d b9 85 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 89 85 0c 00 f7 d8 64 89 01 48
All code
========
   0:	73 01                	jae    0x3
   2:	c3                   	retq   
   3:	48 8b 0d b9 85 0c 00 	mov    0xc85b9(%rip),%rcx        # 0xc85c3
   a:	f7 d8                	neg    %eax
   c:	64 89 01             	mov    %eax,%fs:(%rcx)
   f:	48 83 c8 ff          	or     $0xffffffffffffffff,%rax
  13:	c3                   	retq   
  14:	66 2e 0f 1f 84 00 00 	nopw   %cs:0x0(%rax,%rax,1)
  1b:	00 00 00 
  1e:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
  23:	b8 b0 00 00 00       	mov    $0xb0,%eax
  28:	0f 05                	syscall 
  2a:*	48 3d 01 f0 ff ff    	cmp    $0xfffffffffffff001,%rax		<-- trapping instruction
  30:	73 01                	jae    0x33
  32:	c3                   	retq   
  33:	48 8b 0d 89 85 0c 00 	mov    0xc8589(%rip),%rcx        # 0xc85c3
  3a:	f7 d8                	neg    %eax
  3c:	64 89 01             	mov    %eax,%fs:(%rcx)
  3f:	48                   	rex.W

Code starting with the faulting instruction
===========================================
   0:	48 3d 01 f0 ff ff    	cmp    $0xfffffffffffff001,%rax
   6:	73 01                	jae    0x9
   8:	c3                   	retq   
   9:	48 8b 0d 89 85 0c 00 	mov    0xc8589(%rip),%rcx        # 0xc8599
  10:	f7 d8                	neg    %eax
  12:	64 89 01             	mov    %eax,%fs:(%rcx)
  15:	48                   	rex.W
[  215.224940][ T3608] RSP: 002b:00007ffedaff1e88 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
[  215.225209][ T3608] RAX: ffffffffffffffda RBX: 0000562acd24d150 RCX: 00007f5e44177847
[  215.225467][ T3608] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 0000562acd24d1b8
[  215.225754][ T3608] RBP: 0000000000000000 R08: 1999999999999999 R09: 0000000000000000
[  215.226033][ T3608] R10: 00007f5e441eaac0 R11: 0000000000000206 R12: 0000000000000000
[  215.226303][ T3608] R13: 0000000000000000 R14: 00007ffedaff1ec0 R15: 00007ffedaff3378
[  215.226579][ T3608]  </TASK>
[  215.226794][ T3608] ---[ end trace 0000000000000000 ]---


The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20240219/202402191313.3276317d-oliver.sang@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH v2 3/5] x86/kvm: Make kvm_async_pf_enabled __ro_after_init

[Valentin Schneider]

kvm_async_pf_enabled is only ever enabled in __init kvm_guest_init(), so
mark it as __ro_after_init.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/kernel/kvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index dfe9945b9bece..8f48ce7adfb28 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -44,7 +44,7 @@
 #include <asm/svm.h>
 #include <asm/e820/api.h>
 
-DEFINE_STATIC_KEY_FALSE(kvm_async_pf_enabled);
+DEFINE_STATIC_KEY_FALSE_RO(kvm_async_pf_enabled);
 
 static int kvmapf = 1;
 
-- 
2.43.0

[PATCH v2 4/5] x86/speculation: Make mds_user_clear __ro_after_init

[Valentin Schneider]

mds_user_clear is only ever enabled in:
o __init mds_select_mitigation()
o __init taa_select_mitigation()
o __init mmio_select_mitigation()

mark it as __ro_after_init.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bb0ab8466b919..bab36096015d8 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -112,7 +112,7 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
 DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
 
 /* Control MDS CPU buffer clear before returning to user space */
-DEFINE_STATIC_KEY_FALSE(mds_user_clear);
+DEFINE_STATIC_KEY_FALSE_RO(mds_user_clear);
 EXPORT_SYMBOL_GPL(mds_user_clear);
 /* Control MDS CPU buffer clear before idling (halt, mwait) */
 DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
-- 
2.43.0

[PATCH v2 5/5] x86/tsc: Make __use_tsc __ro_after_init

[Valentin Schneider]

__use_tsc is only ever enabled in __init tsc_enable_sched_clock(), so mark
it as __ro_after_init.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/kernel/tsc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 15f97c0abc9d0..f19b42ea40573 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -44,7 +44,7 @@ EXPORT_SYMBOL(tsc_khz);
 static int __read_mostly tsc_unstable;
 static unsigned int __initdata tsc_early_khz;
 
-static DEFINE_STATIC_KEY_FALSE(__use_tsc);
+static DEFINE_STATIC_KEY_FALSE_RO(__use_tsc);
 
 int tsc_clocksource_reliable;
 
-- 
2.43.0