[RFC Patch 3/7] x86: Introduce MULTIKERNEL_VECTOR for inter-kernel communication

[Cong Wang <xiyou.wangcong@gmail.com>]

From: Cong Wang <cwang@multikernel.io>

This patch adds a dedicated IPI vector (0xea) for multikernel
communication, enabling different kernel instances running on
separate CPUs to send interrupts to each other.

The implementation includes:

- MULTIKERNEL_VECTOR definition at interrupt vector 0xea
- IDT entry declaration and registration for sysvec_multikernel
- Interrupt handler sysvec_multikernel() with proper APIC EOI
  and IRQ statistics tracking
- Placeholder generic_multikernel_interrupt() function for
  extensible multikernel interrupt handling

This vector provides the foundational interrupt mechanism required
for implementing inter-kernel communication protocols in multikernel
environments, where heterogeneous kernel instances coordinate while
maintaining CPU-level isolation.

Signed-off-by: Cong Wang <cwang@multikernel.io>
---
 arch/x86/include/asm/idtentry.h    |  1 +
 arch/x86/include/asm/irq_vectors.h |  1 +
 arch/x86/kernel/idt.c              |  1 +
 arch/x86/kernel/smp.c              | 12 ++++++++++++
 4 files changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index a4ec27c67988..219ee36def33 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -708,6 +708,7 @@ DECLARE_IDTENTRY(RESCHEDULE_VECTOR,			sysvec_reschedule_ipi);
 DECLARE_IDTENTRY_SYSVEC(REBOOT_VECTOR,			sysvec_reboot);
 DECLARE_IDTENTRY_SYSVEC(CALL_FUNCTION_SINGLE_VECTOR,	sysvec_call_function_single);
 DECLARE_IDTENTRY_SYSVEC(CALL_FUNCTION_VECTOR,		sysvec_call_function);
+DECLARE_IDTENTRY_SYSVEC(MULTIKERNEL_VECTOR,			sysvec_multikernel);
 #else
 # define fred_sysvec_reschedule_ipi			NULL
 # define fred_sysvec_reboot				NULL
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 47051871b436..478e2e2d188a 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -102,6 +102,7 @@
  * the host kernel.
  */
 #define POSTED_MSI_NOTIFICATION_VECTOR	0xeb
+#define MULTIKERNEL_VECTOR		0xea
 
 #define NR_VECTORS			 256
 
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index f445bec516a0..063b330d9fbf 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -135,6 +135,7 @@ static const __initconst struct idt_data apic_idts[] = {
 	INTG(RESCHEDULE_VECTOR,			asm_sysvec_reschedule_ipi),
 	INTG(CALL_FUNCTION_VECTOR,		asm_sysvec_call_function),
 	INTG(CALL_FUNCTION_SINGLE_VECTOR,	asm_sysvec_call_function_single),
+	INTG(MULTIKERNEL_VECTOR,		asm_sysvec_multikernel),
 	INTG(REBOOT_VECTOR,			asm_sysvec_reboot),
 #endif
 
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index b014e6d229f9..028cc423a772 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -272,6 +272,18 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_call_function_single)
 	trace_call_function_single_exit(CALL_FUNCTION_SINGLE_VECTOR);
 }
 
+static void generic_multikernel_interrupt(void)
+{
+	pr_info("Multikernel interrupt\n");
+}
+
+DEFINE_IDTENTRY_SYSVEC(sysvec_multikernel)
+{
+	apic_eoi();
+	inc_irq_stat(irq_call_count);
+	generic_multikernel_interrupt();
+}
+
 static int __init nonmi_ipi_setup(char *str)
 {
 	smp_no_nmi_ipi = true;
-- 
2.34.1