mop3/kernel/platform/i386_pc/sys/mm.c

/*
Copyright 2025 Kamil Kowalczyk

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 copyright holder 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
HOLDER 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 <libk/util.h>
#include <libk/types.h>
#include <libk/string.h>
#include <sys/mm.h>
#include <sync/spinlock.h>
#include <mm/bba.h>
#include <mm/pmm.h>
#include <config.h>

#define PD_INDEX(va)  (((va) >> 22) & 0x3FF)
#define PT_INDEX(va)  (((va) >> 12) & 0x3FF)
#define PD_SHIFT 22
#define PT_SHIFT 12

extern char __init_pd;

static struct page_dir *init_pd;

struct page_dir *mm_get_kernel_pd(void) { return init_pd; }

static struct page_dir *mm_alloc_pd(void) {
  struct page_dir *pd = (struct page_dir *)bba_alloc();
  memset(pd, 0, sizeof(*pd));
  sl_init(&pd->sl, "pd");
  pd->pd = (volatile uint32_t *)bba_alloc();
  memset(pd->pt_refcount, 0, sizeof(pd->pt_refcount));
  return pd;
}

static struct page_dir *mm_alloc_existing_pd(uptr_t ptr) {
  struct page_dir *pd = (struct page_dir *)bba_alloc();
  memset(pd, 0, sizeof(*pd));
  sl_init(&pd->sl, "pd");
  pd->pd = (volatile uint32_t *)ptr;
  memset(pd->pt_refcount, 0, sizeof(pd->pt_refcount));
  return pd;
}

void mm_map_page(struct page_dir *pd, uptr_t vaddr, uptr_t paddr, uint32_t flags) {
  if (!(flags & PF_PRESENT))
    return;

  if (flags & PF_LOCK)
    sl_lock(&pd->sl);

  uint32_t pd_idx = PD_INDEX(vaddr);
  uint32_t pt_idx = PT_INDEX(vaddr);
  volatile uint32_t *pt;

  if (!(pd->pd[pd_idx] & PF_PRESENT)) {
    pt = (volatile uint32_t *)bba_alloc();
    if (pt == 0) {
      dbgf("mm_map_page(): run out of BBA memory to alloc a PD\n");
      goto done;
    }

    for (usize_t i = 0; i < PAGE_SIZE/sizeof(uint32_t); i++)
      pt[i] = 0;
    uptr_t phys_pt = (uptr_t)pt - VIRT_BASE;
    pd->pd[pd_idx] = phys_pt | PF_PRESENT | PF_WRITABLE;
    pd->pt_refcount[pd_idx] = 1;
  } else {
    uptr_t pt_phys = pd->pd[pd_idx] & ~(PAGE_SIZE - 1);
    pt = (volatile uint32_t *)(pt_phys + VIRT_BASE);

    if (!(pt[pt_idx] & PF_PRESENT))
      pd->pt_refcount[pd_idx]++;
  }

  pt[pt_idx] = (paddr & ~(PAGE_SIZE - 1)) | (flags & ~PF_LOCK);

done:
  if (flags & PF_LOCK)
    sl_unlock(&pd->sl);
}

void mm_unmap_page(struct page_dir *pd, uptr_t vaddr, uint32_t flags) {
  if (flags & PF_LOCK)
    sl_lock(&pd->sl);

  uint32_t pd_idx = PD_INDEX(vaddr);
  uint32_t pt_idx = PT_INDEX(vaddr);
  volatile uint32_t *pt;

  if (!(pd->pd[pd_idx] & PF_PRESENT)) {
    goto done;
  } else {
    uptr_t pt_phys = pd->pd[pd_idx] & ~(PAGE_SIZE - 1);
    pt = (volatile uint32_t *)(pt_phys + VIRT_BASE);
  }

  if (pt[pt_idx] & PF_PRESENT) {
    pt[pt_idx] &= ~PF_PRESENT;

    if (pd->pt_refcount[pd_idx] > 0)
      pd->pt_refcount[pd_idx]--;

    if (pd->pt_refcount[pd_idx] == 0) {
      bba_free((uptr_t)pt);
      pd->pd[pd_idx] = 0;
    }
  }
  
  __asm__ volatile ("invlpg (%0)" :: "r"(vaddr) : "memory");

done:
  if (flags & PF_LOCK)
    sl_unlock(&pd->sl);
}

uptr_t mm_translate_v2p(struct page_dir *pd, uptr_t vaddr, uint32_t flags) {
  if (flags & PF_LOCK)
    sl_lock(&pd->sl);

  uint32_t pd_idx = PD_INDEX(vaddr);
  uint32_t pt_idx = PT_INDEX(vaddr);
  volatile uint32_t *pt;
  uptr_t paddr = 0;

  if (!(pd->pd[pd_idx] & PF_PRESENT))
    goto done;

  uptr_t pt_phys = pd->pd[pd_idx] & ~(PAGE_SIZE - 1);
  pt = (volatile uint32_t *)(pt_phys + VIRT_BASE);
  if (!(pt[pt_idx] & PF_PRESENT))
    goto done;

  paddr = (pt[pt_idx] & ~(PAGE_SIZE - 1)) | (vaddr & (PAGE_SIZE - 1));

done:
  if (flags & PF_LOCK)
    sl_unlock(&pd->sl);
  return paddr;
}

uptr_t mm_translate_p2v(struct page_dir *pd, uptr_t paddr, uint32_t flags) {
  uptr_t vaddr;
  bool_t found = 0;

  if (flags & PF_LOCK)
    sl_lock(&pd->sl);

  for (uint32_t pd_idx = 0; pd_idx < 1024; pd_idx++) {
    if (!(pd->pd[pd_idx] & PF_PRESENT))
      continue;

    uptr_t pt_phys = pd->pd[pd_idx] & ~(PAGE_SIZE - 1);
    volatile uint32_t *pt = (volatile uint32_t *)(pt_phys + VIRT_BASE);

    for (uint32_t pt_idx = 0; pt_idx < 1024; pt_idx++) {
      if (!(pt[pt_idx] & PF_PRESENT))
        continue;

      uptr_t pt_addr = pt[pt_idx] & ~(PAGE_SIZE - 1);
      if (pt_addr == (paddr & ~(PAGE_SIZE - 1))) {
        vaddr = (pd_idx << PD_SHIFT) | (pt_idx << PT_SHIFT) | (paddr & (PAGE_SIZE - 1));
        found = 1;
        break;
      }
    }

    if (found)
      break;
  }

  if (flags & PF_LOCK)
    sl_unlock(&pd->sl);

  return found ? vaddr : 0;
}

void mm_load_pd(struct page_dir *pd) {
  uptr_t phys = (uptr_t)pd->pd - VIRT_BASE;
  __asm__ volatile ("movl %0, %%cr3" :: "r"(phys));
}

void mm_init(void) {
  init_pd = mm_alloc_existing_pd((uptr_t)&__init_pd);
}