linux-kernel - [RFC Patch v2 05/16] x86: Introduce arch_cpu_physical

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Message-Id: <20251019061631.2235405-6-xiyou.wangcong@gmail.com>
Date: Sat, 18 Oct 2025 23:16:19 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: linux-kernel@...r.kernel.org
Cc: jiri@...nulli.us,
	stefanha@...hat.com,
	multikernel@...ts.linux.dev,
	pasha.tatashin@...een.com,
	Cong Wang <cwang@...tikernel.io>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>,
	Alexander Graf <graf@...zon.com>,
	Mike Rapoport <rppt@...nel.org>,
	Changyuan Lyu <changyuanl@...gle.com>,
	kexec@...ts.infradead.org,
	linux-mm@...ck.org
Subject: [RFC Patch v2 05/16] x86: Introduce arch_cpu_physical_id() to obtain physical CPU ID

From: Cong Wang <cwang@...tikernel.io>

The tranditional smp_processor_id() is a software-defined CPU ID which
is only unique within the same kernel. With Multikernel architecture, we
run multiple Linux kernels on different CPU's, hence the host kernel
needs a globally unique CPU ID to manage the CPU's. The physical CPU ID
is perfect for this case.

This API will be used to globally distinguish CPU's among different
multikernels.

Signed-off-by: Cong Wang <cwang@...tikernel.io>
---
 arch/x86/include/asm/smp.h | 6 ++++++
 arch/x86/kernel/smp.c      | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 1a59fd0de759..378be65ceafa 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -40,6 +40,7 @@ struct smp_ops {
 
 	void (*send_call_func_ipi)(const struct cpumask *mask);
 	void (*send_call_func_single_ipi)(int cpu);
+	int (*cpu_physical_id)(int cpu);
 };
 
 /* Globals due to paravirt */
@@ -100,6 +101,11 @@ static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)
 	smp_ops.send_call_func_ipi(mask);
 }
 
+static inline int arch_cpu_physical_id(int cpu)
+{
+	return smp_ops.cpu_physical_id(cpu);
+}
+
 void cpu_disable_common(void);
 void native_smp_prepare_boot_cpu(void);
 void smp_prepare_cpus_common(void);
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 59658fcd9037..e2eba09da7fc 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -288,6 +288,11 @@ static int __init nonmi_ipi_setup(char *str)
 
 __setup("nonmi_ipi", nonmi_ipi_setup);
 
+static int native_cpu_physical_id(int cpu)
+{
+	return cpu_physical_id(cpu);
+}
+
 struct smp_ops smp_ops = {
 	.smp_prepare_boot_cpu	= native_smp_prepare_boot_cpu,
 	.smp_prepare_cpus	= native_smp_prepare_cpus,
@@ -305,6 +310,7 @@ struct smp_ops smp_ops = {
 
 	.send_call_func_ipi	= native_send_call_func_ipi,
 	.send_call_func_single_ipi = native_send_call_func_single_ipi,
+	.cpu_physical_id	= native_cpu_physical_id,
 };
 EXPORT_SYMBOL_GPL(smp_ops);
 
-- 
2.34.1