[tip: x86/core] x86/preempt: Move preempt count to percpu hot section

["tip-bot2 for Brian Gerst" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     d6bb8b60e0c2be9fb311d6f6ce2530e3dd177450
Gitweb:        https://git.kernel.org/tip/d6bb8b60e0c2be9fb311d6f6ce2530e3dd177450
Author:        Brian Gerst <brgerst@gmail.com>
AuthorDate:    Mon, 03 Mar 2025 11:52:38 -05:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 20:18:02 +01:00

x86/preempt: Move preempt count to percpu hot section

No functional change.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250303165246.2175811-4-brgerst@gmail.com
---
 arch/x86/include/asm/current.h |  1 -
 arch/x86/include/asm/preempt.h | 25 +++++++++++++------------
 arch/x86/kernel/cpu/common.c   |  4 +++-
 include/linux/preempt.h        |  1 +
 4 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
index 60bc66e..46a736d 100644
--- a/arch/x86/include/asm/current.h
+++ b/arch/x86/include/asm/current.h
@@ -14,7 +14,6 @@ struct task_struct;
 
 struct pcpu_hot {
 	struct task_struct	*current_task;
-	int			preempt_count;
 	int			cpu_number;
 #ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING
 	u64			call_depth;
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 919909d..578441d 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -4,10 +4,11 @@
 
 #include <asm/rmwcc.h>
 #include <asm/percpu.h>
-#include <asm/current.h>
 
 #include <linux/static_call_types.h>
 
+DECLARE_PER_CPU_CACHE_HOT(int, __preempt_count);
+
 /* We use the MSB mostly because its available */
 #define PREEMPT_NEED_RESCHED	0x80000000
 
@@ -23,18 +24,18 @@
  */
 static __always_inline int preempt_count(void)
 {
-	return raw_cpu_read_4(pcpu_hot.preempt_count) & ~PREEMPT_NEED_RESCHED;
+	return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
 }
 
 static __always_inline void preempt_count_set(int pc)
 {
 	int old, new;
 
-	old = raw_cpu_read_4(pcpu_hot.preempt_count);
+	old = raw_cpu_read_4(__preempt_count);
 	do {
 		new = (old & PREEMPT_NEED_RESCHED) |
 			(pc & ~PREEMPT_NEED_RESCHED);
-	} while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new));
+	} while (!raw_cpu_try_cmpxchg_4(__preempt_count, &old, new));
 }
 
 /*
@@ -43,7 +44,7 @@ static __always_inline void preempt_count_set(int pc)
 #define init_task_preempt_count(p) do { } while (0)
 
 #define init_idle_preempt_count(p, cpu) do { \
-	per_cpu(pcpu_hot.preempt_count, (cpu)) = PREEMPT_DISABLED; \
+	per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \
 } while (0)
 
 /*
@@ -57,17 +58,17 @@ static __always_inline void preempt_count_set(int pc)
 
 static __always_inline void set_preempt_need_resched(void)
 {
-	raw_cpu_and_4(pcpu_hot.preempt_count, ~PREEMPT_NEED_RESCHED);
+	raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
 }
 
 static __always_inline void clear_preempt_need_resched(void)
 {
-	raw_cpu_or_4(pcpu_hot.preempt_count, PREEMPT_NEED_RESCHED);
+	raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
 }
 
 static __always_inline bool test_preempt_need_resched(void)
 {
-	return !(raw_cpu_read_4(pcpu_hot.preempt_count) & PREEMPT_NEED_RESCHED);
+	return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
 }
 
 /*
@@ -76,12 +77,12 @@ static __always_inline bool test_preempt_need_resched(void)
 
 static __always_inline void __preempt_count_add(int val)
 {
-	raw_cpu_add_4(pcpu_hot.preempt_count, val);
+	raw_cpu_add_4(__preempt_count, val);
 }
 
 static __always_inline void __preempt_count_sub(int val)
 {
-	raw_cpu_add_4(pcpu_hot.preempt_count, -val);
+	raw_cpu_add_4(__preempt_count, -val);
 }
 
 /*
@@ -91,7 +92,7 @@ static __always_inline void __preempt_count_sub(int val)
  */
 static __always_inline bool __preempt_count_dec_and_test(void)
 {
-	return GEN_UNARY_RMWcc("decl", __my_cpu_var(pcpu_hot.preempt_count), e,
+	return GEN_UNARY_RMWcc("decl", __my_cpu_var(__preempt_count), e,
 			       __percpu_arg([var]));
 }
 
@@ -100,7 +101,7 @@ static __always_inline bool __preempt_count_dec_and_test(void)
  */
 static __always_inline bool should_resched(int preempt_offset)
 {
-	return unlikely(raw_cpu_read_4(pcpu_hot.preempt_count) == preempt_offset);
+	return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
 }
 
 #ifdef CONFIG_PREEMPTION
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f00870b..a9d6153 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2066,12 +2066,14 @@ __setup("setcpuid=", setup_setcpuid);
 
 DEFINE_PER_CPU_CACHE_HOT(struct pcpu_hot, pcpu_hot) = {
 	.current_task	= &init_task,
-	.preempt_count	= INIT_PREEMPT_COUNT,
 	.top_of_stack	= TOP_OF_INIT_STACK,
 };
 EXPORT_PER_CPU_SYMBOL(pcpu_hot);
 EXPORT_PER_CPU_SYMBOL(const_pcpu_hot);
 
+DEFINE_PER_CPU_CACHE_HOT(int, __preempt_count) = INIT_PREEMPT_COUNT;
+EXPORT_PER_CPU_SYMBOL(__preempt_count);
+
 #ifdef CONFIG_X86_64
 static void wrmsrl_cstar(unsigned long val)
 {
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index ca86235..4c1af9b 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -319,6 +319,7 @@ do { \
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 
 struct preempt_notifier;
+struct task_struct;
 
 /**
  * preempt_ops - notifiers called when a task is preempted and rescheduled