分页（多页）场景下跨页地址访问映射机制咨询

Great question—this cuts right to how x86 paging operates at its core, so let’s break it down plainly:

Short Answer #

Your program P1 will NOT automatically map to the second page if it accesses an address beyond the first page’s upper limit. Instead, the CPU will immediately trigger a page fault interrupt (#PF, interrupt number 14).

Detailed Explanation #

Here’s why this works the way it does:

• x86 paging is an explicit mapping system, not an implicit or auto-filling one. Every virtual address your program uses must have a corresponding, valid entry in the page tables (starting with the page directory pointed to by CR3).
• When you registered two non-contiguous pages in the page directory, you only created mappings for those specific virtual address ranges. Any virtual address outside those ranges has no valid entry in the page tables.
• When P1 tries to access an unmapped address:
  1. The CPU checks the relevant page directory entry (and page table entry, if using 2-level paging) for that virtual address.
  2. Since there’s no valid entry (either the entry is missing, or the Present bit P is set to 0), the CPU raises a page fault.
  3. The kernel’s page fault handler will then handle this—usually by either allocating a new physical page and setting up the mapping, or terminating the program if the access is invalid.

There’s no logic in the CPU that assumes "if you have a mapping for page X, you must want page X+1 mapped to the next physical page". Every single virtual-to-physical mapping has to be explicitly configured in the page tables.

内容的提问来源于stack exchange，提问作者Leosa99 _