KirkOS/src/arch/x86_64/sys/apic.c

#include "apic.h"
#include "mm/vmm.h"
#include "mm/memory.h"
#include "arch/x86_64/cpu/io.h"
#include "libk/stdio.h"
/* ── Internal state ───────────────────────────────────────────────────────── */
static volatile uint32_t *g_lapic = NULL;   /* Virtual address of LAPIC MMIO */

/* ── Low-level helpers ────────────────────────────────────────────────────── */

static inline uint32_t lapic_read(uint32_t reg) {
    return g_lapic[reg >> 2];
}

static inline void lapic_write(uint32_t reg, uint32_t val) {
    g_lapic[reg >> 2] = val;
    /* Serialise: read back a read-only register to ensure the write landed
     * before we continue (required by the APIC spec).                       */
    (void)g_lapic[LAPIC_ID >> 2];
}

static inline void rdmsr(uint32_t msr, uint32_t *lo, uint32_t *hi) {
    asm volatile("rdmsr" : "=a"(*lo), "=d"(*hi) : "c"(msr));
}

static inline void wrmsr(uint32_t msr, uint32_t lo, uint32_t hi) {
    asm volatile("wrmsr" : : "a"(lo), "d"(hi), "c"(msr));
}

/* ── Public API ───────────────────────────────────────────────────────────── */

uint64_t lapic_get_phys_base(void) {
    uint32_t lo, hi;
    rdmsr(IA32_APIC_BASE_MSR, &lo, &hi);
    /* Physical base is in bits [35:12] of the 64-bit MSR */
    return ((uint64_t)(hi & 0xFu) << 32) | (lo & 0xFFFFF000u);
}

void lapic_eoi(void) {
    lapic_write(LAPIC_EOI, 0);
}

uint32_t lapic_id(void) {
    /* On xAPIC the LAPIC ID sits in bits [31:24] of the ID register */
    return lapic_read(LAPIC_ID) >> 24;
}

void lapic_init(void) {
    /*
     * ── Step 1: Re-enable the APIC global enable bit ─────────────────────
     *
     * Earlier in kmain (before pmm_init) we cleared bit 11 of IA32_APIC_BASE
     * so that the i8259 PIC would raise interrupts properly under Limine.
     * Now that the LAPIC is being brought online we must restore that bit;
     * without it the LAPIC is completely off and nothing below will work.
     */
    uint32_t lo, hi;
    rdmsr(IA32_APIC_BASE_MSR, &lo, &hi);
    lo |= IA32_APIC_BASE_ENABLE;
    wrmsr(IA32_APIC_BASE_MSR, lo, hi);

    /*
     * ── Step 2: Locate the LAPIC MMIO window ─────────────────────────────
     *
     * The physical address is almost always 0xFEE00000 but we read it from
     * the MSR to be correct.  vmm_init() already identity-maps all physical
     * memory through the HHDM (up to 256 GiB), so the MMIO page is reachable
     * at phys + MEM_PHYS_OFFSET with no extra mapping needed.
     *
     * TODO: For strict correctness the LAPIC page should be mapped as
     *       uncacheable (PAT / PCD).  In practice, QEMU / BOCHS work fine
     *       because MTRRs mark the 0xFEE00000 range as UC by default.
     */
    uint64_t phys_base = ((uint64_t)(hi & 0xFu) << 32) | (lo & 0xFFFFF000u);
    printf("[LAPIC] Physical base: 0x%08x%08x\n",
           (uint32_t)(phys_base >> 32), (uint32_t)phys_base);

    g_lapic = (volatile uint32_t *)(phys_base + MEM_PHYS_OFFSET);

    /*
     * ── Step 3: Software-enable the LAPIC via the SVR ────────────────────
     *
     * Bit 8 = Software Enable.  The lower 8 bits are the "spurious interrupt
     * vector" delivered if the CPU acknowledges an interrupt that was
     * retracted by the LAPIC; 0xFF is the conventional choice.
     */
    lapic_write(LAPIC_SVR, LAPIC_SVR_ENABLE | 0xFF);

    /*
     * ── Step 4: Configure LINT0 as ExtINT (i8259 pass-through) ──────────
     *
     * On a standard PC the i8259 INTR pin is wired to the BSP's LINT0.
     * Setting LINT0 to ExtINT delivery mode makes the LAPIC act as a
     * transparent relay: the i8259 interrupt acknowledge cycle goes through
     * normally, the full 8-bit vector comes from the i8259, and the CPU's
     * existing IDT entries + irq.c EOI code all keep working unchanged.
     *
     * This is the "Virtual Wire" mode described in the Intel MP Spec.
     */
    lapic_write(LAPIC_LVT_LINT0, LAPIC_LVT_DM_EXTINT);

    /*
     * ── Step 5: Configure LINT1 as NMI ───────────────────────────────────
     *
     * LINT1 is the NMI pin on standard PCs.  Delivery mode = 4 (NMI),
     * unmasked, edge-triggered (the default when LAPIC_LVT_LEVEL is clear).
     */
    lapic_write(LAPIC_LVT_LINT1, LAPIC_LVT_DM_NMI);

    /*
     * ── Step 6: Mask LVT entries we are not yet using ────────────────────
     *
     * Timer, error, and (if present) thermal / perf entries all start masked.
     * Assign distinct vectors in the 0xF0-0xFE range so that if one fires
     * spuriously the IDT handler can identify it and send EOI.
     */
    lapic_write(LAPIC_LVT_TIMER, LAPIC_LVT_MASKED | 0xFD);
    lapic_write(LAPIC_LVT_ERROR, LAPIC_LVT_MASKED | 0xFE);

    /* Version register: bits [23:16] = max LVT entry index */
    uint32_t ver     = lapic_read(LAPIC_VER);
    uint32_t max_lvt = (ver >> 16) & 0xFF;
    if (max_lvt >= 4) lapic_write(LAPIC_LVT_THERMAL, LAPIC_LVT_MASKED | 0xFC);
    if (max_lvt >= 5) lapic_write(LAPIC_LVT_PERF,    LAPIC_LVT_MASKED | 0xFB);

    /*
     * ── Step 7: Clear the Error Status Register ───────────────────────────
     *
     * The APIC spec requires writing ESR twice to clear stale error bits.
     */
    lapic_write(LAPIC_ESR, 0);
    lapic_write(LAPIC_ESR, 0);

    /* Dismiss any stale in-service interrupt */
    lapic_write(LAPIC_EOI, 0);

    /*
     * ── Step 8: Set Task Priority to 0 ───────────────────────────────────
     *
     * TPR = 0 means the CPU will accept all interrupt priorities.
     * Raise this later if need to block lower-priority interrupts.
     */
    lapic_write(LAPIC_TPR, 0);

    printf("[LAPIC] Online. ID=%u  version=0x%02x  max_lvt=%u\n",
           lapic_id(), ver & 0xFF, max_lvt);
}