kernel: sched: Add initial sched related code

Signed-off-by: Ian Moffett <ian@osmora.org>

11 files changed, 454 insertions, 5 deletions

diff --git a/sys/arch/amd64/amd64/cpu.c b/sys/arch/amd64/amd64/cpu.c
index 8763b51..0c59730 100644
--- a/sys/arch/amd64/amd64/cpu.c
+++ b/sys/arch/amd64/amd64/cpu.c
@@ -27,7 +27,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <machine/cpu.h>
+#include <machine/cpu_mp.h>
 #include <sys/cdefs.h>
 
 __KERNEL_META("$Hyra$: cpu.c, Ian Marco Moffett, "
@@ -49,5 +49,12 @@ amd64_get_bsp(void)
 struct cpu_info *
 amd64_this_cpu(void)
 {
-    return amd64_get_bsp();
+    struct cpu_ctx *cctx;
+
+    if (!mp_supported()) {
+        return amd64_get_bsp();
+    }
+
+    cctx = (void *)read_gs_base();
+    return cctx->ci;
 }
diff --git a/sys/arch/amd64/amd64/cpu_mp.c b/sys/arch/amd64/amd64/cpu_mp.c
new file mode 100644
index 0000000..c382439
--- /dev/null
+++ b/sys/arch/amd64/amd64/cpu_mp.c
@@ -0,0 +1,133 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/cpu_mp.h>
+#include <sys/machdep.h>
+#include <sys/limine.h>
+#include <sys/types.h>
+#include <sys/syslog.h>
+#include <sys/sched.h>
+#include <sys/cpu.h>
+#include <vm/dynalloc.h>
+#include <assert.h>
+
+__MODULE_NAME("cpu_mp");
+__KERNEL_META("$Hyra$: cpu_mp.c, Ian Marco Moffett, "
+              "SMP related code");
+
+static volatile struct limine_smp_request g_smp_req = {
+    .id = LIMINE_SMP_REQUEST,
+    .revision = 0
+};
+
+static bool is_mp_supported = false;
+
+static void
+ap_create_cctx(struct cpu_info *ci)
+{
+    struct cpu_ctx *cctx;
+
+    cctx = dynalloc(sizeof(struct cpu_ctx));
+    __assert(cctx != NULL);
+
+    cctx->ci = ci;
+
+    /* Set *our* %GS now... */
+    wrmsr(IA32_KERNEL_GS_BASE, (uintptr_t)cctx);
+
+    if (!is_mp_supported) {
+        is_mp_supported = true;
+    }
+}
+
+static void
+ap_trampoline(struct limine_smp_info *si)
+{
+    struct cpu_info *ci;
+
+    ci = (void *)si->extra_argument;
+
+    pre_init();
+    ap_create_cctx(ci);
+    processor_init();
+
+    sched_init_processor(ci);
+
+    /* Should not be reached */
+    __assert(0);
+    __builtin_unreachable();
+}
+
+/*
+ * Returns true if SMP is supported.
+ */
+bool
+mp_supported(void)
+{
+    return is_mp_supported;
+}
+
+void
+ap_bootstrap(struct cpu_info *ci)
+{
+    struct limine_smp_response *resp = g_smp_req.response;
+    struct limine_smp_info **cpus;
+    struct cpu_info *ap_ci = NULL;
+    size_t cpu_init_counter;
+
+    /* Should not happen */
+    __assert(resp != NULL);
+
+    cpus = resp->cpus;
+    cpu_init_counter = resp->cpu_count - 1;
+
+    if (resp->cpu_count == 1) {
+        /* TODO: Allow single core processing */
+        panic("System only has 1 core!\n");
+    }
+
+    /* Create processor context */
+    ap_create_cctx(ci);
+
+    KINFO("Bootstrapping %d cores...\n", cpu_init_counter);
+    for (size_t i = 0; i < resp->cpu_count; ++i) {
+        if (ci->id == cpus[i]->lapic_id) {
+            KINFO("Skip %d (BSP)... continue\n", ci->id);
+            continue;
+        }
+
+        ap_ci = dynalloc(sizeof(struct cpu_info));
+        __assert(ap_ci != NULL);
+        cpu_attach(ap_ci);
+
+        cpus[i]->extra_argument = (uintptr_t)dynalloc(sizeof(struct cpu_info));
+        cpus[i]->goto_address = ap_trampoline;
+    }
+    KINFO("AP bootstrap done for all cores\n");
+}
diff --git a/sys/include/arch/amd64/cpu.h b/sys/include/arch/amd64/cpu.h
index 37ad69d..c72c106 100644
--- a/sys/include/arch/amd64/cpu.h
+++ b/sys/include/arch/amd64/cpu.h
@@ -33,7 +33,10 @@
 #include <sys/types.h>
 #include <sys/cdefs.h>
 #include <sys/spinlock.h>
+#include <sys/sched_state.h>
+#include <sys/queue.h>
 #include <machine/tss.h>
+#include <machine/msr.h>
 
 #define this_cpu()      amd64_this_cpu()
 #define get_bsp()       amd64_get_bsp()
@@ -52,7 +55,10 @@ struct cpu_info {
     /* Per-arch fields  */
     void *pmap;                         /* Current pmap */
     uint32_t id;
+    uint32_t idx;
     struct spinlock lock;
+    struct sched_state sched_state;
+    TAILQ_ENTRY(cpu_info) link;
 
     /* AMD64 */
     volatile size_t lapic_tmr_freq;
@@ -62,6 +68,16 @@ struct cpu_info {
 };
 
 /*
+ * Contains information for the current
+ * core. Stored in %GS.
+ *
+ * MUST REMAIN IN ORDER!!!
+ */
+struct cpu_ctx {
+    struct cpu_info *ci;
+};
+
+/*
  * Returns true for this core if maskable
  * interrupts are masked (CLI) and false if
  * they aren't (STI).
@@ -75,6 +91,18 @@ amd64_is_intr_mask(void)
     return __TEST(flags, 1 << 9);
 }
 
+static inline void
+write_gs_base(uintptr_t val)
+{
+    wrmsr(IA32_KERNEL_GS_BASE, val);
+}
+
+static inline uintptr_t
+read_gs_base(void)
+{
+    return rdmsr(IA32_KERNEL_GS_BASE);
+}
+
 struct cpu_info *amd64_this_cpu(void);
 struct cpu_info *amd64_get_bsp(void);
 
diff --git a/sys/include/arch/amd64/cpu_mp.h b/sys/include/arch/amd64/cpu_mp.h
new file mode 100644
index 0000000..4047f3b
--- /dev/null
+++ b/sys/include/arch/amd64/cpu_mp.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_CPU_AP_H_
+#define _SYS_CPU_AP_H_
+
+#include <machine/cpu.h>
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__weak void ap_bootstrap(struct cpu_info *ci);
+__weak bool mp_supported(void);
+
+#endif  /* !_SYS_CPU_AP_H_ */
diff --git a/sys/include/arch/amd64/msr.h b/sys/include/arch/amd64/msr.h
index 64a790c..d36548b 100644
--- a/sys/include/arch/amd64/msr.h
+++ b/sys/include/arch/amd64/msr.h
@@ -33,7 +33,8 @@
 #include <sys/types.h>
 #include <sys/cdefs.h>
 
-#define IA32_SPEC_CTL   0x00000048
+#define IA32_SPEC_CTL       0x00000048
+#define IA32_KERNEL_GS_BASE 0xC0000102
 
 static inline uint64_t
 rdmsr(uint32_t msr_addr)
diff --git a/sys/include/sys/proc.h b/sys/include/sys/proc.h
new file mode 100644
index 0000000..1c0e389
--- /dev/null
+++ b/sys/include/sys/proc.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_PROC_H_
+#define _SYS_PROC_H_
+
+#include <sys/types.h>
+#include <sys/queue.h>
+#include <machine/cpu.h>
+
+/*
+ * A task running on the CPU e.g., a process or
+ * a thread.
+ */
+struct proc {
+    pid_t pid;
+    struct cpu_info *cpu;
+    TAILQ_ENTRY(tailq_entry) entries;
+};
+
+#endif  /* !_SYS_PROC_H_ */
diff --git a/sys/include/sys/sched.h b/sys/include/sys/sched.h
new file mode 100644
index 0000000..4fdf065
--- /dev/null
+++ b/sys/include/sys/sched.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_SCHED_H_
+#define _SYS_SCHED_H_
+
+#include <sys/proc.h>
+#include <sys/queue.h>
+#include <sys/types.h>
+#include <sys/spinlock.h>
+#include <machine/cpu.h>
+
+__noreturn
+void sched_init_processor(struct cpu_info *ci);
+
+#endif  /* !_SYS_SCHED_H_ */
diff --git a/sys/include/sys/sched_state.h b/sys/include/sys/sched_state.h
new file mode 100644
index 0000000..03a55dd
--- /dev/null
+++ b/sys/include/sys/sched_state.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_SCHED_STATE_H_
+#define _SYS_SCHED_STATE_H_
+
+#include <sys/types.h>
+#include <sys/queue.h>
+
+/*
+ * Scheduler state, per CPU.
+ */
+struct sched_state {
+    TAILQ_HEAD(, proc) queue;
+    size_t queue_nrun;          /* Number of processes in the run queue */
+};
+
+#endif /* !_SYS_SCHED_STATE_H_ */
diff --git a/sys/include/sys/types.h b/sys/include/sys/types.h
index 29f4421..388458c 100644
--- a/sys/include/sys/types.h
+++ b/sys/include/sys/types.h
@@ -65,6 +65,7 @@ typedef int32_t     ssize_t;        /* Byte count or error */
 typedef _Bool bool;
 typedef ssize_t off_t;
 typedef size_t uintptr_t;
+typedef int pid_t;
 
 #if defined(_KERNEL)
 typedef uintptr_t vaddr_t;      /* Virtual address */
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index 99f1e87..2fe84ed 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -32,6 +32,8 @@
 #include <sys/syslog.h>
 #include <sys/machdep.h>
 #include <sys/timer.h>
+#include <sys/sched.h>
+#include <machine/cpu_mp.h>
 #include <firmware/acpi/acpi.h>
 #include <vm/physseg.h>
 #include <logo.h>
@@ -72,6 +74,8 @@ list_timers(void)
 void
 main(void)
 {
+    struct cpu_info *ci;
+
     pre_init();
     tty_init();
     syslog_init();
@@ -86,6 +90,11 @@ main(void)
     processor_init();
     list_timers();
 
-    /* We're done here, halt the processor */
-    __ASMV("cli; hlt");
+    ci = this_cpu();
+    if (ap_bootstrap != NULL) {
+        ap_bootstrap(ci);
+    }
+
+    sched_init_processor(ci);
+    __builtin_unreachable();
 }
diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
new file mode 100644
index 0000000..da4c6c5
--- /dev/null
+++ b/sys/kern/kern_sched.c
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/sched.h>
+#include <sys/sched_state.h>
+#include <sys/types.h>
+#include <sys/cdefs.h>
+#include <sys/spinlock.h>
+#include <assert.h>
+
+/*
+ * This is the processor ready list, processors
+ * (cores) that have no task assigned live here.
+ *
+ * Assigning a task to a core is done by popping from
+ * this list. However, it must be done carefully and
+ * must be serialized. You *must* acquire ci_ready_lock
+ * before performing *any* operations on ci_ready_list!!!
+ */
+static TAILQ_HEAD(, cpu_info) ci_ready_list;
+static struct spinlock ci_ready_lock = {0};
+
+/*
+ * Push a processor into the ready list.
+ */
+static void
+sched_enqueue_ci(struct cpu_info *ci)
+{
+    spinlock_acquire(&ci_ready_lock);
+    TAILQ_INSERT_TAIL(&ci_ready_list, ci, link);
+    spinlock_release(&ci_ready_lock);
+}
+
+/*
+ * Processor awaiting tasks to be assigned will be here spinning.
+ *
+ * XXX: We are not using the PAUSE instruction for the sake of
+ *      ensuring compatibility... PAUSE is F3 90, REP NOP is
+ *      F3 90... REP NOP will be read as a PAUSE on processors
+ *      that support it.
+ */
+__noreturn static void
+sched_enter(void)
+{
+    for (;;) {
+        __ASMV("rep; nop");
+    }
+}
+
+/*
+ * Setup scheduler related things and enqueue AP.
+ */
+void
+sched_init_processor(struct cpu_info *ci)
+{
+    struct sched_state *sched_state = &ci->sched_state;
+    static bool is_init = true;
+
+    if (is_init) {
+        /* Setup ready list if first call */
+        TAILQ_INIT(&ci_ready_list);
+        is_init = false;
+    }
+
+    TAILQ_INIT(&sched_state->queue);
+    sched_enqueue_ci(ci);
+
+    sched_enter();
+
+    __builtin_unreachable();
+}