linux-kernel - [RFC PATCH 03/11] x86/smp: Move cpu number to percpu hot section

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Message-ID: <20250222190623.262689-4-brgerst@gmail.com>
Date: Sat, 22 Feb 2025 14:06:15 -0500
From: Brian Gerst <brgerst@...il.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Ard Biesheuvel <ardb@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Brian Gerst <brgerst@...il.com>
Subject: [RFC PATCH 03/11] x86/smp: Move cpu number to percpu hot section

No functional change.

Signed-off-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/include/asm/current.h | 1 -
 arch/x86/include/asm/smp.h     | 7 ++++---
 arch/x86/kernel/setup_percpu.c | 5 ++++-
 kernel/bpf/verifier.c          | 4 ++--
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
index 9a2fe2fd7d74..119099431c76 100644
--- a/arch/x86/include/asm/current.h
+++ b/arch/x86/include/asm/current.h
@@ -16,7 +16,6 @@ struct pcpu_hot {
 	union {
 		struct {
 			struct task_struct	*current_task;
-			int			cpu_number;
 #ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING
 			u64			call_depth;
 #endif
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index ca073f40698f..a249f9991708 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -5,9 +5,10 @@
 #include <linux/cpumask.h>
 
 #include <asm/cpumask.h>
-#include <asm/current.h>
 #include <asm/thread_info.h>
 
+DECLARE_PER_CPU_HOT(int, cpu_number);
+
 DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
 DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
 DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_die_map);
@@ -133,8 +134,8 @@ __visible void smp_call_function_single_interrupt(struct pt_regs *r);
  * This function is needed by all SMP systems. It must _always_ be valid
  * from the initial startup.
  */
-#define raw_smp_processor_id()  this_cpu_read(pcpu_hot.cpu_number)
-#define __smp_processor_id() __this_cpu_read(pcpu_hot.cpu_number)
+#define raw_smp_processor_id()  this_cpu_read(cpu_number)
+#define __smp_processor_id() __this_cpu_read(cpu_number)
 
 #ifdef CONFIG_X86_32
 extern int safe_smp_processor_id(void);
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 1e7be9409aa2..0ea3443433c5 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -23,6 +23,9 @@
 #include <asm/cpumask.h>
 #include <asm/cpu.h>
 
+DEFINE_PER_CPU_HOT(int, cpu_number);
+EXPORT_PER_CPU_SYMBOL(cpu_number);
+
 DEFINE_PER_CPU_READ_MOSTLY(unsigned long, this_cpu_off);
 EXPORT_PER_CPU_SYMBOL(this_cpu_off);
 
@@ -161,7 +164,7 @@ void __init setup_per_cpu_areas(void)
 	for_each_possible_cpu(cpu) {
 		per_cpu_offset(cpu) = delta + pcpu_unit_offsets[cpu];
 		per_cpu(this_cpu_off, cpu) = per_cpu_offset(cpu);
-		per_cpu(pcpu_hot.cpu_number, cpu) = cpu;
+		per_cpu(cpu_number, cpu) = cpu;
 		setup_percpu_segment(cpu);
 		/*
 		 * Copy data used in early init routines from the
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03adfd5..604134d33282 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21687,12 +21687,12 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		if (insn->imm == BPF_FUNC_get_smp_processor_id &&
 		    verifier_inlines_helper_call(env, insn->imm)) {
 			/* BPF_FUNC_get_smp_processor_id inlining is an
-			 * optimization, so if pcpu_hot.cpu_number is ever
+			 * optimization, so if cpu_number is ever
 			 * changed in some incompatible and hard to support
 			 * way, it's fine to back out this inlining logic
 			 */
 #ifdef CONFIG_SMP
-			insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
+			insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&cpu_number);
 			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
 			insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
 			cnt = 3;
-- 
2.48.1