/* $OpenBSD: pte.h,v 1.7 2004/02/06 00:23:21 deraadt 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 ) * 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_ */