/* $OpenBSD: pte.h,v 1.9 2007/02/20 21:15:01 tom Exp $ */
/* $NetBSD: pte.h,v 1.11 1998/02/06 21:58:05 thorpej Exp $ */
/*
*
* Copyright (c) 1997 Charles D. Cranor and Washington University.
* All rights reserved.
*
* 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgment:
* This product includes software developed by Charles D. Cranor and
* Washington University.
* 4. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/
/*
* pte.h rewritten by chuck based on the jolitz version, plus random
* info on the pentium and other processors found on the net. the
* goal of this rewrite is to provide enough documentation on the MMU
* hardware that the reader will be able to understand it without having
* to refer to a hardware manual.
*/
#ifndef _I386_PTE_H_
#define _I386_PTE_H_
/*
* i386 MMU hardware structure:
*
* the i386 MMU is a two-level MMU which maps 4GB of virtual memory.
* the pagesize is 4K (4096 [0x1000] bytes), although newer pentium
* processors can support a 4MB pagesize as well.
*
* the first level table (segment table?) is called a "page directory"
* and it contains 1024 page directory entries (PDEs). each PDE is
* 4 bytes (an int), so a PD fits in a single 4K page. this page is
* the page directory page (PDP). each PDE in a PDP maps 4MB of space
* (1024 * 4MB = 4GB). a PDE contains the physical address of the
* second level table: the page table. or, if 4MB pages are being used,
* then the PDE contains the PA of the 4MB page being mapped.
*
* a page table consists of 1024 page table entries (PTEs). each PTE is
* 4 bytes (an int), so a page table also fits in a single 4K page. a
* 4K page being used as a page table is called a page table page (PTP).
* each PTE in a PTP maps one 4K page (1024 * 4K = 4MB). a PTE contains
* the physical address of the page it maps and some flag bits (described
* below).
*
* the processor has a special register, "cr3", which points to the
* the PDP which is currently controlling the mappings of the virtual
* address space.
*
* the following picture shows the translation process for a 4K page:
*
* %cr3 register [PA of PDP]
* |
* |
* | bits <31-22> of VA bits <21-12> of VA bits <11-0>
* | index the PDP (0 - 1023) index the PTP are the page offset
* | | | |
* | v | |
* +--->+----------+ | |
* | PD Page | PA of v |
* | |---PTP-------->+------------+ |
* | 1024 PDE | | page table |--PTE--+ |
* | entries | | (aka PTP) | | |
* +----------+ | 1024 PTE | | |
* | entries | | |
* +------------+ | |
* | |
* bits <31-12> bits <11-0>
* p h y s i c a l a d d r
*
* the i386 caches PTEs in a TLB. it is important to flush out old
* TLB mappings when making a change to a mappings. writing to the
* %cr3 will flush the entire TLB. newer processors also have an
* instruction that will invalidate the mapping of a single page (which
* is useful if you are changing a single mappings because it preserves
* all the cached TLB entries).
*
* as shows, bits 31-12 of the PTE contain PA of the page being mapped.
* the rest of the PTE is defined as follows:
* bit# name use
* 11 n/a available for OS use, hardware ignores it
* 10 n/a available for OS use, hardware ignores it
* 9 n/a available for OS use, hardware ignores it
* 8 G global bit (see discussion below)
* 7 PS page size [for PDEs] (0=4k, 1=4M <if supported>)
* 6 D dirty (modified) page
* 5 A accessed (referenced) page
* 4 PCD cache disable
* 3 PWT prevent write through (cache)
* 2 U/S user/supervisor bit (0=supervisor only, 1=both u&s)
* 1 R/W read/write bit (0=read only, 1=read-write)
* 0 P present (valid)
*
* notes:
* - on the i386 the R/W bit is ignored if processor is in supervisor
* state (bug!)
* - PS is only supported on newer processors
* - PTEs with the G bit are global in the sense that they are not
* flushed from the TLB when %cr3 is written (to flush, use the
* "flush single page" instruction). this is only supported on
* newer processors. this bit can be used to keep the kernel's
* TLB entries around while context switching. since the kernel
* is mapped into all processes at the same place it does not make
* sense to flush these entries when switching from one process'
* pmap to another.
*/
#if !defined(_LOCORE)
/*
* here we define the data types for PDEs and PTEs
*/
typedef u_int32_t pd_entry_t; /* PDE */
typedef u_int32_t pt_entry_t; /* PTE */
#endif
/*
* now we define various for playing with virtual addresses
*/
#define PDSHIFT 22 /* offset of PD index in VA */
#define NBPD (1 << PDSHIFT) /* # bytes mapped by PD (4MB) */
#define PDOFSET (NBPD-1) /* mask for non-PD part of VA */
#if 0 /* not used? */
#define NPTEPD (NBPD / NBPG) /* # of PTEs in a PD */
#else
#define PTES_PER_PTP (NBPD / NBPG) /* # of PTEs in a PTP */
#endif
#define PD_MASK 0xffc00000 /* page directory address bits */
#define PT_MASK 0x003ff000 /* page table address bits */
/*
* here we define the bits of the PDE/PTE, as described above:
*
* XXXCDC: need to rename these (PG_u == ugly).
*/
#define PG_V 0x00000001 /* valid entry */
#define PG_RO 0x00000000 /* read-only page */
#define PG_RW 0x00000002 /* read-write page */
#define PG_u 0x00000004 /* user accessible page */
#define PG_PROT 0x00000806 /* all protection bits */
#define PG_N 0x00000018 /* non-cacheable */
#define PG_U 0x00000020 /* has been used */
#define PG_M 0x00000040 /* has been modified */
#define PG_PS 0x00000080 /* 4MB page size */
#define PG_G 0x00000100 /* global, don't TLB flush */
#define PG_AVAIL1 0x00000200 /* ignored by hardware */
#define PG_AVAIL2 0x00000400 /* ignored by hardware */
#define PG_AVAIL3 0x00000800 /* ignored by hardware */
#define PG_FRAME 0xfffff000 /* page frame mask */
#define PG_LGFRAME 0xffc00000 /* large (4M) page frame mask */
/*
* various short-hand protection codes
*/
#define PG_KR 0x00000000 /* kernel read-only */
#define PG_KW 0x00000002 /* kernel read-write */
/*
* page protection exception bits
*/
#define PGEX_P 0x01 /* protection violation (vs. no mapping) */
#define PGEX_W 0x02 /* exception during a write cycle */
#define PGEX_U 0x04 /* exception while in user mode (upl) */
#define PGEX_I 0x10 /* instruction fetch blocked by NX */
#endif /* _I386_PTE_H_ */
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