Page Fault Error Code X86
Contents |
EiB). Paging is a system which allows each process to see the full virtual address space, without actually requiring the full amount of physical memory to be available or present. In fact, current implementations of x86-64 have a limit of 1 TiB and a theoretical limit of
X86 Exceptions
4 PiB of physical RAM. In addition to this, paging introduces the benefit of page-level protection. exception 13 general protection fault In this system, user processes can only see and modify data which is paged in on their own address space, providing hardware-based isolation. System pages general protection fault error code are also protected from user processes. On the x86-64 architecture, page-level protection now completely supersedes Segmentation as the memory protection mechanism. On the IA-32 architecture, both paging and segmentation exist, but segmentation is now considered 'legacy'. Once an Operating System
X86 Exception Handling
has paging, it can also make use of other benefits and workarounds, such as linear framebuffer simulation for memory-mapped IO and paging out to disk, where disk storage space is used to free up physical RAM. Contents 1 MMU 1.1 Page Directory 1.2 Page Table 1.3 Example 2 Enabling 3 Physical Address Extension 4 Usage 4.1 Virtual Address Spaces 4.2 Virtual Memory 5 Manipulation 6 Page Faults 6.1 Handling 7 INVLPG 8 Paging Tricks 9 See Also 9.1 Articles 9.2 External Links
X86 Page Table Entry
MMU Paging is achieved through the use of the MMU (temporary: article 1, article 2). On the x86, the MMU maps memory through a series of tables, two to be exact. They are the paging directory (PD), and the paging table (PT). Both tables contain 1024 4-byte entries, making them 4 KiB each. In the page directory, each entry points to a page table. In the page table, each entry points to a physical address that is then mapped to the virtual address found by calculating the offset within the directory and the offset within the table. This can be done as the entire table system represents a linear 4-GiB virtual memory map. Page Directory The topmost paging structure is the page directory. It is essentially an array of page directory entries that take the following form. A Page Directory Entry The page table address field represents the physical address of the page table that manages the four megabytes at that point. Please note that it is very important that this address be 4-KiB aligned. This is needed, due to the fact that the last 12 bits of the 32-bit value are overwritten by access bits and such. S, or 'Page Size' stores the page size for that specific entry. If the bit is set, then pages are 4 MiB in size. Otherwise, they are 4 KiB. Please note that 4-MiB pages require PSE to be enabled. A, or 'Accessed' is used to di
my Stack Overflow answer. Sample code Intel manual Application Hardware implementation Paging vs segmentation Example: simplified single-level paging scheme Page tables Page table x86 paging tutorial entries Address translation in single-level scheme Page fault Simplifications Example: multi-level
Invalid Opcode Exception X64 Exception Type 06
paging scheme Address translation in multi-level scheme 64-bit architectures PAE PSE PAE and PSE page table linux general protection fault schemes TLB Basic operation Replacement policy CAM Invalidating entries Linux kernel usage Kernel vs process memory layout Process memory layout Source tree Memory management unit Other architectures Bibliography http://wiki.osdev.org/Paging Sample code Minimal example: https://github.com/cirosantilli/x86-bare-metal-examples/blob/5c672f73884a487414b3e21bd9e579c67cd77621/paging.S Like everything else in programming, the only way to really understand this is to play with minimal examples. What makes this a “hard” subject is that the minimal example is large because you need to make your own small OS. Intel manual Although it is impossible to understand without examples http://www.cirosantilli.com/x86-paging/ in mind, try to get familiar with the manuals as soon as possible. Intel describes paging in the Intel Manual Volume 3 System Programming Guide - 325384-056US September 2015 Chapter 4 “Paging”. Specially interesting is Figure 4-4 “Formats of CR3 and Paging-Structure Entries with 32-Bit Paging”, which gives the key data structures. Application Paging makes it easier to compile and run two programs at the same time on a single computer. For example, when you compile two programs, the compiler does not know if they are going to be running at the same time or not. So nothing prevents it from using the same RAM address, say, 0x1234, to store a global variable. But if two programs use the same address and run at the same time, this is obviously going to break them! Paging solves this problem beautifully by adding one degree of indirection: (logical) ------------> (physical) paging Compilers don’t need to worry about other programs: they just use simple logical addres
1 /* 2 * Copyright (C) 1995 Linus Torvalds 3 * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs. 4 * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar 5 */ 6 #include