kern/amd64: cpu: Add initial SMP startup code

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

1 files changed, 129 insertions, 0 deletions

diff --git a/src/sys/arch/amd64/cpu/cpu_mp.c b/src/sys/arch/amd64/cpu/cpu_mp.c
new file mode 100644
index 0000000..293e449
--- /dev/null
+++ b/src/sys/arch/amd64/cpu/cpu_mp.c
@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * 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 the project 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/cdefs.h>
+#include <sys/param.h>
+#include <sys/syslog.h>
+#include <sys/panic.h>
+#include <sys/cpuvar.h>
+#include <sys/limits.h>
+#include <os/kalloc.h>
+#include <os/spinlock.h>
+#include <machine/mdcpu.h>
+#include <string.h>
+#include <limine.h>
+
+extern struct pcore g_bsp;
+
+static size_t ncores_up = 1;
+static struct pcore *corelist[CPU_MAX];
+static struct spinlock lock;
+
+/*
+ * We'll use the bootloader to keep the kernel small
+ *
+ * XXX: Maybe move this somewhere better?
+ */
+static volatile struct limine_smp_request g_smp_req = {
+    .id = LIMINE_SMP_REQUEST,
+    .revision = 0
+};
+
+__dead static void
+ap_entry(struct limine_smp_info *)
+{
+    struct pcore *pcore;
+
+    spinlock_acquire(&lock);
+    pcore = kalloc(sizeof(*pcore));
+    if (kalloc == NULL) {
+        panic("mp: could not allocate pcore\n");
+    }
+
+    /* Initialize the core */
+    memset(pcore, 0, sizeof(*pcore));
+    pcore->id = ncores_up;
+    cpu_conf(pcore);
+    cpu_init(pcore);
+
+    corelist[ncores_up++] = pcore;
+    spinlock_release(&lock);
+    for (;;);
+}
+
+void
+bsp_ap_startup(void)
+{
+    struct limine_smp_response *resp = g_smp_req.response;
+    struct limine_smp_info **cpus;
+    struct mdcore *mdcore;
+    uint32_t ncores, tmp;
+
+    /* Sanity check */
+    if (__unlikely(resp == NULL)) {
+        panic("mp: could not get SMP response\n");
+    }
+
+    /* Put the AP list in a known state */
+    memset(corelist, 0, sizeof(*corelist));
+    corelist[0] = &g_bsp;
+
+    /*
+     * If the number of cores total exceeds the cap we have
+     * set in sys/limits.h, truncate what we start up and
+     * log it so any inconsistencies have a definitive
+     * source.
+     */
+    cpus = resp->cpus;
+    ncores = MIN(resp->cpu_count, CPU_MAX);
+    if (resp->cpu_count >= CPU_MAX) {
+        tmp = (resp->cpu_count - ncores - 1);
+        printf("mp: not starting %d cores\n", tmp);
+    }
+
+    /* Don't continue if we have only one core */
+    if (ncores == 1) {
+        printf("mp: single cored CPU - no APs to bring up\n");
+        return;
+    }
+
+    printf("mp: bringing APs online...\n");
+    mdcore = &g_bsp.md;
+
+    for (int i = 0; i < ncores; ++i) {
+        if (mdcore->apic_id == cpus[i]->lapic_id) {
+            continue;
+        }
+
+        cpus[i]->goto_address = ap_entry;
+    }
+
+    while (ncores_up < ncores);
+    printf("mp: %d cores [up]\n", ncores - 1);
+}