144 lines
5.7 KiB
C
144 lines
5.7 KiB
C
/*
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* arch/arm/include/asm/pgtable-2level.h
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*
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* Copyright (C) 1995-2002 Russell King
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#ifndef _ASM_PGTABLE_2LEVEL_H
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#define _ASM_PGTABLE_2LEVEL_H
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/*
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* Hardware-wise, we have a two level page table structure, where the first
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* level has 4096 entries, and the second level has 256 entries. Each entry
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* is one 32-bit word. Most of the bits in the second level entry are used
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* by hardware, and there aren't any "accessed" and "dirty" bits.
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*
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* Linux on the other hand has a three level page table structure, which can
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* be wrapped to fit a two level page table structure easily - using the PGD
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* and PTE only. However, Linux also expects one "PTE" table per page, and
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* at least a "dirty" bit.
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*
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* Therefore, we tweak the implementation slightly - we tell Linux that we
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* have 2048 entries in the first level, each of which is 8 bytes (iow, two
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* hardware pointers to the second level.) The second level contains two
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* hardware PTE tables arranged contiguously, preceded by Linux versions
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* which contain the state information Linux needs. We, therefore, end up
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* with 512 entries in the "PTE" level.
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*
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* This leads to the page tables having the following layout:
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*
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* pgd pte
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* | |
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* +--------+
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* | | +------------+ +0
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* +- - - - + | Linux pt 0 |
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* | | +------------+ +1024
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* +--------+ +0 | Linux pt 1 |
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* | |-----> +------------+ +2048
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* +- - - - + +4 | h/w pt 0 |
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* | |-----> +------------+ +3072
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* +--------+ +8 | h/w pt 1 |
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* | | +------------+ +4096
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*
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* See L_PTE_xxx below for definitions of bits in the "Linux pt", and
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* PTE_xxx for definitions of bits appearing in the "h/w pt".
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*
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* PMD_xxx definitions refer to bits in the first level page table.
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*
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* The "dirty" bit is emulated by only granting hardware write permission
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* iff the page is marked "writable" and "dirty" in the Linux PTE. This
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* means that a write to a clean page will cause a permission fault, and
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* the Linux MM layer will mark the page dirty via handle_pte_fault().
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* For the hardware to notice the permission change, the TLB entry must
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* be flushed, and ptep_set_access_flags() does that for us.
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*
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* The "accessed" or "young" bit is emulated by a similar method; we only
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* allow accesses to the page if the "young" bit is set. Accesses to the
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* page will cause a fault, and handle_pte_fault() will set the young bit
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* for us as long as the page is marked present in the corresponding Linux
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* PTE entry. Again, ptep_set_access_flags() will ensure that the TLB is
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* up to date.
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*
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* However, when the "young" bit is cleared, we deny access to the page
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* by clearing the hardware PTE. Currently Linux does not flush the TLB
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* for us in this case, which means the TLB will retain the transation
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* until either the TLB entry is evicted under pressure, or a context
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* switch which changes the user space mapping occurs.
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*/
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#define PTRS_PER_PTE 512
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#define PTRS_PER_PMD 1
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#define PTRS_PER_PGD 2048
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#define PTE_HWTABLE_PTRS (PTRS_PER_PTE)
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#define PTE_HWTABLE_OFF (PTE_HWTABLE_PTRS * sizeof(pte_t))
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#define PTE_HWTABLE_SIZE (PTRS_PER_PTE * sizeof(u32))
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/*
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* PMD_SHIFT determines the size of the area a second-level page table can map
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* PGDIR_SHIFT determines what a third-level page table entry can map
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*/
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#define PMD_SHIFT 21
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#define PGDIR_SHIFT 21
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#define PMD_SIZE (1UL << PMD_SHIFT)
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#define PMD_MASK (~(PMD_SIZE-1))
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#define PGDIR_SIZE (1UL << PGDIR_SHIFT)
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#define PGDIR_MASK (~(PGDIR_SIZE-1))
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/*
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* section address mask and size definitions.
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*/
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#define SECTION_SHIFT 20
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#define SECTION_SIZE (1UL << SECTION_SHIFT)
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#define SECTION_MASK (~(SECTION_SIZE-1))
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/*
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* ARMv6 supersection address mask and size definitions.
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*/
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#define SUPERSECTION_SHIFT 24
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#define SUPERSECTION_SIZE (1UL << SUPERSECTION_SHIFT)
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#define SUPERSECTION_MASK (~(SUPERSECTION_SIZE-1))
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#define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE)
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/*
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* "Linux" PTE definitions.
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*
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* We keep two sets of PTEs - the hardware and the linux version.
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* This allows greater flexibility in the way we map the Linux bits
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* onto the hardware tables, and allows us to have YOUNG and DIRTY
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* bits.
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*
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* The PTE table pointer refers to the hardware entries; the "Linux"
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* entries are stored 1024 bytes below.
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*/
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#define L_PTE_PRESENT (_AT(pteval_t, 1) << 0)
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#define L_PTE_YOUNG (_AT(pteval_t, 1) << 1)
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#define L_PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !PRESENT */
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#define L_PTE_DIRTY (_AT(pteval_t, 1) << 6)
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#define L_PTE_RDONLY (_AT(pteval_t, 1) << 7)
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#define L_PTE_USER (_AT(pteval_t, 1) << 8)
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#define L_PTE_XN (_AT(pteval_t, 1) << 9)
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#define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */
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/*
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* These are the memory types, defined to be compatible with
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* pre-ARMv6 CPUs cacheable and bufferable bits: XXCB
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*/
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#define L_PTE_MT_UNCACHED (_AT(pteval_t, 0x00) << 2) /* 0000 */
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#define L_PTE_MT_BUFFERABLE (_AT(pteval_t, 0x01) << 2) /* 0001 */
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#define L_PTE_MT_WRITETHROUGH (_AT(pteval_t, 0x02) << 2) /* 0010 */
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#define L_PTE_MT_WRITEBACK (_AT(pteval_t, 0x03) << 2) /* 0011 */
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#define L_PTE_MT_MINICACHE (_AT(pteval_t, 0x06) << 2) /* 0110 (sa1100, xscale) */
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#define L_PTE_MT_WRITEALLOC (_AT(pteval_t, 0x07) << 2) /* 0111 */
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#define L_PTE_MT_DEV_SHARED (_AT(pteval_t, 0x04) << 2) /* 0100 */
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#define L_PTE_MT_DEV_NONSHARED (_AT(pteval_t, 0x0c) << 2) /* 1100 */
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#define L_PTE_MT_DEV_WC (_AT(pteval_t, 0x09) << 2) /* 1001 */
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#define L_PTE_MT_DEV_CACHED (_AT(pteval_t, 0x0b) << 2) /* 1011 */
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#define L_PTE_MT_MASK (_AT(pteval_t, 0x0f) << 2)
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#endif /* _ASM_PGTABLE_2LEVEL_H */
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