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#include "memory.h"
#include <kernel/memory/paging.h>
/*
* kernel virtual space guarantees
*
* 1. there are two kernel page directories, one each for the lower and upper
* GiB of space. they are self-mapped as tables in the trailing entries
* of the table for the upper space. these must exist.
* 2. because of (1.) the kernel page tables (directoires inclusive) occupy
* the upper 4MiB of kernel address space.
* 3. the kernel is always at the beginning of its virtual space.
* currently this is 0xffffffff80000000 but that may change
* 4. the entry stack's head is always -4MiB from the end of the address space.
* its size is currently 64KiB. this may change.
*/
#define kpde_index(v) ((v >> (PAGE_MAP_BITS + PAGE_OFFSET_BITS)) & 0x3ff)
#define kpte_index(v) ((v >> PAGE_OFFSET_BITS) & 0x7ffff)
extern char k_virt_base;
extern char k_text_begin;
extern char k_text_end;
extern char k_data_begin;
extern char k_data_end;
static uint64_t *const kernel_ptes = (uint64_t *)0xffffffffffc00000;
static uint64_t *const kernel_pdes = (uint64_t *)0xffffffffffffe000;
// we can track 4GiB of physical pages with this bitmap.
#define PAGE_BITMAP_ENTRIES 16384
#define PAGE_BITMAP_WIDTH 64
static uint64_t page_bitmap[PAGE_BITMAP_ENTRIES];
static phys_addr_t bitmap_alloc(void)
{
static uint64_t *page_bitmap_last = NULL;
if (!page_bitmap_last || !*page_bitmap_last)
{
for (int i = 0; i < PAGE_BITMAP_ENTRIES; i++)
{
if (page_bitmap[i])
{
page_bitmap_last = &page_bitmap[i];
break;
}
}
}
int index = page_bitmap_last - page_bitmap;
int bit = __builtin_ffsll(*page_bitmap_last);
return (index * PAGE_BITMAP_WIDTH + bit) * PAGE_SIZE;
}
static void bitmap_free(phys_addr_t page)
{
int index = (page >> PAGE_OFFSET_BITS) / PAGE_BITMAP_WIDTH;
int bit = (page >> PAGE_OFFSET_BITS) % PAGE_BITMAP_WIDTH;
page_bitmap[index] |= (1 << bit);
}
/*
static virt_addr_t virtual_alloc(void)
{
}
static void virtual_free(virt_addr_t vpage)
{
}
*/
static uint64_t *get_kernel_pde(virt_addr_t vaddr)
{
return &kernel_pdes[kpde_index(vaddr)];
}
static uint64_t *get_kernel_pte(uint64_t vaddr)
{
return &kernel_ptes[kpte_index(vaddr)];
}
void memory_init()
{
}
phys_addr_t page_alloc(void)
{
return bitmap_alloc();
}
void page_free(phys_addr_t page)
{
bitmap_free(page);
}
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