linux-kernel - [RFC Patch 5/7] x86: Introduce arch_cpu_physical

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Message-Id: <20250918222607.186488-6-xiyou.wangcong@gmail.com>
Date: Thu, 18 Sep 2025 15:26:04 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: linux-kernel@...r.kernel.org
Cc: 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 5/7] 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 ++++++
 kernel/multikernel.c       | 9 +++++----
 3 files changed, 17 insertions(+), 4 deletions(-)

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 3ee515e32383..face9f80e05c 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -289,6 +289,11 @@ 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,
@@ -306,6 +311,7 @@ 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);
 
diff --git a/kernel/multikernel.c b/kernel/multikernel.c
index 74e2f84b7914..7f6f90485876 100644
--- a/kernel/multikernel.c
+++ b/kernel/multikernel.c
@@ -150,7 +150,7 @@ int multikernel_send_ipi_data(int cpu, void *data, size_t data_size, unsigned lo
 
 	/* Set header information */
 	target->data_size = data_size;
-	target->sender_cpu = smp_processor_id();
+	target->sender_cpu = arch_cpu_physical_id(smp_processor_id());
 	target->type = type;
 
 	/* Copy the actual data into the buffer */
@@ -175,6 +175,7 @@ static void multikernel_interrupt_handler(void)
 	struct mk_ipi_data *data;
 	struct mk_ipi_handler *handler;
 	int current_cpu = smp_processor_id();
+	int current_physical_id = arch_cpu_physical_id(current_cpu);
 
 	/* Ensure shared memory is initialized */
 	if (!mk_shared_mem) {
@@ -183,10 +184,10 @@ static void multikernel_interrupt_handler(void)
 	}
 
 	/* Get this CPU's data area from shared memory */
-	data = &mk_shared_mem->cpu_data[current_cpu];
+	data = &mk_shared_mem->cpu_data[current_physical_id];
 
-	pr_debug("Multikernel IPI received on CPU %d from CPU %d, type=%u\n",
-		 current_cpu, data->sender_cpu, data->type);
+	pr_info("Multikernel IPI received on CPU %d (physical id %d) from CPU %d type=%u\n",
+		 current_cpu, current_physical_id, data->sender_cpu, data->type);
 
     raw_spin_lock(&mk_handlers_lock);
     for (handler = mk_handlers; handler; handler = handler->next) {
-- 
2.34.1