1/*
  2 *  arch/arm/include/asm/pgtable-2level.h
  3 *
  4 *  Copyright (C) 1995-2002 Russell King
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License version 2 as
  8 * published by the Free Software Foundation.
  9 */
 10#ifndef _ASM_PGTABLE_2LEVEL_H
 11#define _ASM_PGTABLE_2LEVEL_H
 12
 13/*
 14 * Hardware-wise, we have a two level page table structure, where the first
 15 * level has 4096 entries, and the second level has 256 entries.  Each entry
 16 * is one 32-bit word.  Most of the bits in the second level entry are used
 17 * by hardware, and there aren't any "accessed" and "dirty" bits.
 18 *
 19 * Linux on the other hand has a three level page table structure, which can
 20 * be wrapped to fit a two level page table structure easily - using the PGD
 21 * and PTE only.  However, Linux also expects one "PTE" table per page, and
 22 * at least a "dirty" bit.
 23 *
 24 * Therefore, we tweak the implementation slightly - we tell Linux that we
 25 * have 2048 entries in the first level, each of which is 8 bytes (iow, two
 26 * hardware pointers to the second level.)  The second level contains two
 27 * hardware PTE tables arranged contiguously, preceded by Linux versions
 28 * which contain the state information Linux needs.  We, therefore, end up
 29 * with 512 entries in the "PTE" level.
 30 *
 31 * This leads to the page tables having the following layout:
 32 *
 33 *    pgd             pte
 34 * |        |
 35 * +--------+
 36 * |        |       +------------+ +0
 37 * +- - - - +       | Linux pt 0 |
 38 * |        |       +------------+ +1024
 39 * +--------+ +0    | Linux pt 1 |
 40 * |        |-----> +------------+ +2048
 41 * +- - - - + +4    |  h/w pt 0  |
 42 * |        |-----> +------------+ +3072
 43 * +--------+ +8    |  h/w pt 1  |
 44 * |        |       +------------+ +4096
 45 *
 46 * See L_PTE_xxx below for definitions of bits in the "Linux pt", and
 47 * PTE_xxx for definitions of bits appearing in the "h/w pt".
 48 *
 49 * PMD_xxx definitions refer to bits in the first level page table.
 50 *
 51 * The "dirty" bit is emulated by only granting hardware write permission
 52 * iff the page is marked "writable" and "dirty" in the Linux PTE.  This
 53 * means that a write to a clean page will cause a permission fault, and
 54 * the Linux MM layer will mark the page dirty via handle_pte_fault().
 55 * For the hardware to notice the permission change, the TLB entry must
 56 * be flushed, and ptep_set_access_flags() does that for us.
 57 *
 58 * The "accessed" or "young" bit is emulated by a similar method; we only
 59 * allow accesses to the page if the "young" bit is set.  Accesses to the
 60 * page will cause a fault, and handle_pte_fault() will set the young bit
 61 * for us as long as the page is marked present in the corresponding Linux
 62 * PTE entry.  Again, ptep_set_access_flags() will ensure that the TLB is
 63 * up to date.
 64 *
 65 * However, when the "young" bit is cleared, we deny access to the page
 66 * by clearing the hardware PTE.  Currently Linux does not flush the TLB
 67 * for us in this case, which means the TLB will retain the transation
 68 * until either the TLB entry is evicted under pressure, or a context
 69 * switch which changes the user space mapping occurs.
 70 */
 71#define PTRS_PER_PTE		512
 72#define PTRS_PER_PMD		1
 73#define PTRS_PER_PGD		2048
 74
 75#define PTE_HWTABLE_PTRS	(PTRS_PER_PTE)
 76#define PTE_HWTABLE_OFF		(PTE_HWTABLE_PTRS * sizeof(pte_t))
 77#define PTE_HWTABLE_SIZE	(PTRS_PER_PTE * sizeof(u32))
 78
 79/*
 80 * PMD_SHIFT determines the size of the area a second-level page table can map
 81 * PGDIR_SHIFT determines what a third-level page table entry can map
 82 */
 83#define PMD_SHIFT		21
 84#define PGDIR_SHIFT		21
 85
 86#define PMD_SIZE		(1UL << PMD_SHIFT)
 87#define PMD_MASK		(~(PMD_SIZE-1))
 88#define PGDIR_SIZE		(1UL << PGDIR_SHIFT)
 89#define PGDIR_MASK		(~(PGDIR_SIZE-1))
 90
 91/*
 92 * section address mask and size definitions.
 93 */
 94#define SECTION_SHIFT		20
 95#define SECTION_SIZE		(1UL << SECTION_SHIFT)
 96#define SECTION_MASK		(~(SECTION_SIZE-1))
 97
 98/*
 99 * ARMv6 supersection address mask and size definitions.
100 */
101#define SUPERSECTION_SHIFT	24
102#define SUPERSECTION_SIZE	(1UL << SUPERSECTION_SHIFT)
103#define SUPERSECTION_MASK	(~(SUPERSECTION_SIZE-1))
104
105#define USER_PTRS_PER_PGD	(TASK_SIZE / PGDIR_SIZE)
106
107/*
108 * "Linux" PTE definitions.
109 *
110 * We keep two sets of PTEs - the hardware and the linux version.
111 * This allows greater flexibility in the way we map the Linux bits
112 * onto the hardware tables, and allows us to have YOUNG and DIRTY
113 * bits.
114 *
115 * The PTE table pointer refers to the hardware entries; the "Linux"
116 * entries are stored 1024 bytes below.
117 */
118#define L_PTE_PRESENT		(_AT(pteval_t, 1) << 0)
119#define L_PTE_YOUNG		(_AT(pteval_t, 1) << 1)
120#define L_PTE_FILE		(_AT(pteval_t, 1) << 2)	/* only when !PRESENT */
121#define L_PTE_DIRTY		(_AT(pteval_t, 1) << 6)
122#define L_PTE_RDONLY		(_AT(pteval_t, 1) << 7)
123#define L_PTE_USER		(_AT(pteval_t, 1) << 8)
124#define L_PTE_XN		(_AT(pteval_t, 1) << 9)
125#define L_PTE_SHARED		(_AT(pteval_t, 1) << 10)	/* shared(v6), coherent(xsc3) */
126
127/*
128 * These are the memory types, defined to be compatible with
129 * pre-ARMv6 CPUs cacheable and bufferable bits:   XXCB
130 */
131#define L_PTE_MT_UNCACHED	(_AT(pteval_t, 0x00) << 2)	/* 0000 */
132#define L_PTE_MT_BUFFERABLE	(_AT(pteval_t, 0x01) << 2)	/* 0001 */
133#define L_PTE_MT_WRITETHROUGH	(_AT(pteval_t, 0x02) << 2)	/* 0010 */
134#define L_PTE_MT_WRITEBACK	(_AT(pteval_t, 0x03) << 2)	/* 0011 */
135#define L_PTE_MT_MINICACHE	(_AT(pteval_t, 0x06) << 2)	/* 0110 (sa1100, xscale) */
136#define L_PTE_MT_WRITEALLOC	(_AT(pteval_t, 0x07) << 2)	/* 0111 */
137#define L_PTE_MT_DEV_SHARED	(_AT(pteval_t, 0x04) << 2)	/* 0100 */
138#define L_PTE_MT_DEV_NONSHARED	(_AT(pteval_t, 0x0c) << 2)	/* 1100 */
139#define L_PTE_MT_DEV_WC		(_AT(pteval_t, 0x09) << 2)	/* 1001 */
140#define L_PTE_MT_DEV_CACHED	(_AT(pteval_t, 0x0b) << 2)	/* 1011 */
141#define L_PTE_MT_MASK		(_AT(pteval_t, 0x0f) << 2)
142
143#ifndef __ASSEMBLY__
144
145/*
146 * The "pud_xxx()" functions here are trivial when the pmd is folded into
147 * the pud: the pud entry is never bad, always exists, and can't be set or
148 * cleared.
149 */
150#define pud_none(pud)		(0)
151#define pud_bad(pud)		(0)
152#define pud_present(pud)	(1)
153#define pud_clear(pudp)		do { } while (0)
154#define set_pud(pud,pudp)	do { } while (0)
155
156static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
157{
158	return (pmd_t *)pud;
159}
160
161#define pmd_bad(pmd)		(pmd_val(pmd) & 2)
162
163#define copy_pmd(pmdpd,pmdps)		\
164	do {				\
165		pmdpd[0] = pmdps[0];	\
166		pmdpd[1] = pmdps[1];	\
167		flush_pmd_entry(pmdpd);	\
168	} while (0)
169
170#define pmd_clear(pmdp)			\
171	do {				\
172		pmdp[0] = __pmd(0);	\
173		pmdp[1] = __pmd(0);	\
174		clean_pmd_entry(pmdp);	\
175	} while (0)
176
177/* we don't need complex calculations here as the pmd is folded into the pgd */
178#define pmd_addr_end(addr,end) (end)
179
180#define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
181
182#endif /* __ASSEMBLY__ */
183
184#endif /* _ASM_PGTABLE_2LEVEL_H */