From cf1bb5e566ad0e346af810b399d871a74031feb2 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Fri, 25 Jul 2025 02:44:11 -0400
Subject: kernel/amd64: Keep track of which cores are online

Give each core a bit that indicates whether the core is online or
halted. We also provide a cpu_halt() which marks the core as offline.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/amd64/machdep.c |  1 +
 sys/include/arch/amd64/cdefs.h |  3 ++-
 sys/include/arch/amd64/cpu.h   | 16 ++++++++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

(limited to 'sys')

diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index efd1af8..19dcf44 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -418,6 +418,7 @@ cpu_startup(struct cpu_info *ci)
     setup_vectors(ci);
 
     try_mitigate_spectre();
+    ci->online = 1;
 
     cpu_get_info(ci);
     cpu_enable_smep();
diff --git a/sys/include/arch/amd64/cdefs.h b/sys/include/arch/amd64/cdefs.h
index a49736b..d038a15 100644
--- a/sys/include/arch/amd64/cdefs.h
+++ b/sys/include/arch/amd64/cdefs.h
@@ -31,6 +31,7 @@
 #define _AMD64_CDEFS_H_
 
 #include <sys/cdefs.h>
+#include <machine/cpu.h>
 
 /*
  * Please use CLI wisely, it is a good idea to use
@@ -40,7 +41,7 @@
 #define md_pause()  __ASMV("rep; nop")      /* (F3 90) PAUSE */
 #define md_intoff() __ASMV("cli")           /* Clear interrupts */
 #define md_inton()  __ASMV("sti")           /* Enable interrupts */
-#define md_hlt()    __ASMV("hlt")           /* Halt the processor */
+#define md_hlt() cpu_halt()                 /* Halt the processor */
 
 /*
  * AMD64 specific defines
diff --git a/sys/include/arch/amd64/cpu.h b/sys/include/arch/amd64/cpu.h
index 046b621..116661b 100644
--- a/sys/include/arch/amd64/cpu.h
+++ b/sys/include/arch/amd64/cpu.h
@@ -36,6 +36,7 @@
 #include <sys/sched.h>
 #include <sys/spinlock.h>
 #include <machine/tss.h>
+#include <machine/cdefs.h>
 
 #define CPU_IRQ(IRQ_N) (BIT((IRQ_N)) & 0xFF)
 
@@ -51,6 +52,7 @@ struct cpu_info {
     uint8_t family : 4;         /* CPU family ID */
     uint8_t has_x2apic : 1;
     uint8_t tlb_shootdown : 1;
+    uint8_t online : 1;         /* CPU online */
     uint8_t ipl;
     size_t lapic_tmr_freq;
     uint8_t irq_mask;
@@ -80,4 +82,18 @@ void mp_bootstrap_aps(struct cpu_info *ci);
 
 extern struct cpu_info g_bsp_ci;
 
+__always_inline static inline void
+cpu_halt(void)
+{
+    struct cpu_info *ci = this_cpu();
+
+    if (ci != NULL)
+        ci->online = 0;
+
+    __ASMV("hlt");
+
+    if (ci != NULL)
+        ci->online = 1;
+}
+
 #endif  /* !_MACHINE_CPU_H_ */
-- 
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