rulimine/stage23/mm/vmm.c

#include <stdint.h>
#include <stddef.h>
#include <mm/vmm.h>
#include <mm/pmm.h>
#include <lib/blib.h>
#include <sys/cpu.h>

#define PT_SIZE ((uint64_t)0x1000)

typedef uint64_t pt_entry_t;

void vmm_assert_nx(void) {
    uint32_t a, b, c, d;
    if (!cpuid(0x80000001, 0, &a, &b, &c, &d) || !(d & (1 << 20))) {
        panic(false, "vmm: NX functionality not available on this CPU.");
    }
}

static pt_entry_t *get_next_level(pt_entry_t *current_level, size_t entry) {
    pt_entry_t *ret;

    if (current_level[entry] & 0x1) {
        // Present flag set
        ret = (pt_entry_t *)(size_t)(current_level[entry] & ~((pt_entry_t)0xfff));
    } else {
        // Allocate a table for the next level
        ret = ext_mem_alloc(PT_SIZE);
        // Present + writable + user (0b111)
        current_level[entry] = (pt_entry_t)(size_t)ret | 0b111;
    }

    return ret;
}

pagemap_t new_pagemap(int lv) {
    pagemap_t pagemap;
    pagemap.levels    = lv;
    pagemap.top_level = ext_mem_alloc(PT_SIZE);
    return pagemap;
}

void map_page(pagemap_t pagemap, uint64_t virt_addr, uint64_t phys_addr, uint64_t flags, enum page_size pg_size) {
    // Calculate the indices in the various tables using the virtual address
    size_t pml5_entry = (virt_addr & ((uint64_t)0x1ff << 48)) >> 48;
    size_t pml4_entry = (virt_addr & ((uint64_t)0x1ff << 39)) >> 39;
    size_t pml3_entry = (virt_addr & ((uint64_t)0x1ff << 30)) >> 30;
    size_t pml2_entry = (virt_addr & ((uint64_t)0x1ff << 21)) >> 21;
    size_t pml1_entry = (virt_addr & ((uint64_t)0x1ff << 12)) >> 12;

    pt_entry_t *pml5, *pml4, *pml3, *pml2, *pml1;

    // Paging levels
    switch (pagemap.levels) {
        case 5:
            pml5 = pagemap.top_level;
            goto level5;
        case 4:
            pml4 = pagemap.top_level;
            goto level4;
        default:
            __builtin_unreachable();
    }

level5:
    pml4 = get_next_level(pml5, pml5_entry);
level4:
    pml3 = get_next_level(pml4, pml4_entry);
    pml2 = get_next_level(pml3, pml3_entry);

    if (pg_size == Size2MiB) {
        pml2[pml2_entry] = (pt_entry_t)(phys_addr | flags | (1 << 7));
        return;
    }

    pml1 = get_next_level(pml2, pml2_entry);

    pml1[pml1_entry] = (pt_entry_t)(phys_addr | flags);
}