[RFC Patch v2 05/16] x86: Introduce arch_cpu_physical_id() to obtain physical CPU ID

Cong Wang
2025-10-19T06:16:59Z

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@multikernel.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