Method FindPageTableEntry

src/memory/virtual_memory.cpp:298–340

}

auto VirtualMemory::FindPageTableEntry(void* page_dir, void* virtual_addr,
                                       bool allocate) -> Expected<uint64_t*> {
  auto* current_table = reinterpret_cast<uint64_t*>(page_dir);
  auto vaddr = reinterpret_cast<uint64_t>(virtual_addr);

  // 遍历页表层级
  for (size_t level = cpu_io::virtual_memory::kPageTableLevels - 1; level > 0;
       --level) {
    // 获取当前级别的虚拟页号
    auto vpn = cpu_io::virtual_memory::GetVirtualPageNumber(vaddr, level);
    auto* pte = &current_table[vpn];
    if (cpu_io::virtual_memory::IsPageTableEntryValid(*pte)) {
      // 页表项有效，获取下一级页表
      current_table = reinterpret_cast<uint64_t*>(
          cpu_io::virtual_memory::PageTableEntryToPhysical(*pte));
    } else {
      // 页表项无效
      if (allocate) {
        auto* new_table = aligned_alloc(cpu_io::virtual_memory::kPageSize,
                                        cpu_io::virtual_memory::kPageSize);
        if (new_table == nullptr) {
          return std::unexpected(Error(ErrorCode::kVmAllocationFailed));
        }
        // 清零新页表
        std::memset(new_table, 0, cpu_io::virtual_memory::kPageSize);

        // 设置中间页表项
        *pte = cpu_io::virtual_memory::PhysicalToPageTableEntry(
            reinterpret_cast<uint64_t>(new_table),
            cpu_io::virtual_memory::GetTableEntryPermissions());

        current_table = reinterpret_cast<uint64_t*>(new_table);
      } else {
        return std::unexpected(Error(ErrorCode::kVmPageNotMapped));
      }
    }
  }

  // 返回最底层页表中的页表项
  auto vpn = cpu_io::virtual_memory::GetVirtualPageNumber(vaddr, 0);

  return &current_table[vpn];
}