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Diffstat (limited to 'arch/arm/include/asm/pgtable-2level.h')
| -rw-r--r-- | arch/arm/include/asm/pgtable-2level.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h new file mode 100644 index 00000000000..470457e1cfc --- /dev/null +++ b/arch/arm/include/asm/pgtable-2level.h @@ -0,0 +1,143 @@ +/* + * arch/arm/include/asm/pgtable-2level.h + * + * Copyright (C) 1995-2002 Russell King + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ +#ifndef _ASM_PGTABLE_2LEVEL_H +#define _ASM_PGTABLE_2LEVEL_H + +/* + * Hardware-wise, we have a two level page table structure, where the first + * level has 4096 entries, and the second level has 256 entries. Each entry + * is one 32-bit word. Most of the bits in the second level entry are used + * by hardware, and there aren't any "accessed" and "dirty" bits. + * + * Linux on the other hand has a three level page table structure, which can + * be wrapped to fit a two level page table structure easily - using the PGD + * and PTE only. However, Linux also expects one "PTE" table per page, and + * at least a "dirty" bit. + * + * Therefore, we tweak the implementation slightly - we tell Linux that we + * have 2048 entries in the first level, each of which is 8 bytes (iow, two + * hardware pointers to the second level.) The second level contains two + * hardware PTE tables arranged contiguously, preceded by Linux versions + * which contain the state information Linux needs. We, therefore, end up + * with 512 entries in the "PTE" level. + * + * This leads to the page tables having the following layout: + * + * pgd pte + * | | + * +--------+ + * | | +------------+ +0 + * +- - - - + | Linux pt 0 | + * | | +------------+ +1024 + * +--------+ +0 | Linux pt 1 | + * | |-----> +------------+ +2048 + * +- - - - + +4 | h/w pt 0 | + * | |-----> +------------+ +3072 + * +--------+ +8 | h/w pt 1 | + * | | +------------+ +4096 + * + * See L_PTE_xxx below for definitions of bits in the "Linux pt", and + * PTE_xxx for definitions of bits appearing in the "h/w pt". + * + * PMD_xxx definitions refer to bits in the first level page table. + * + * The "dirty" bit is emulated by only granting hardware write permission + * iff the page is marked "writable" and "dirty" in the Linux PTE. This + * means that a write to a clean page will cause a permission fault, and + * the Linux MM layer will mark the page dirty via handle_pte_fault(). + * For the hardware to notice the permission change, the TLB entry must + * be flushed, and ptep_set_access_flags() does that for us. + * + * The "accessed" or "young" bit is emulated by a similar method; we only + * allow accesses to the page if the "young" bit is set. Accesses to the + * page will cause a fault, and handle_pte_fault() will set the young bit + * for us as long as the page is marked present in the corresponding Linux + * PTE entry. Again, ptep_set_access_flags() will ensure that the TLB is + * up to date. + * + * However, when the "young" bit is cleared, we deny access to the page + * by clearing the hardware PTE. Currently Linux does not flush the TLB + * for us in this case, which means the TLB will retain the transation + * until either the TLB entry is evicted under pressure, or a context + * switch which changes the user space mapping occurs. + */ +#define PTRS_PER_PTE 512 +#define PTRS_PER_PMD 1 +#define PTRS_PER_PGD 2048 + +#define PTE_HWTABLE_PTRS (PTRS_PER_PTE) +#define PTE_HWTABLE_OFF (PTE_HWTABLE_PTRS * sizeof(pte_t)) +#define PTE_HWTABLE_SIZE (PTRS_PER_PTE * sizeof(u32)) + +/* + * PMD_SHIFT determines the size of the area a second-level page table can map + * PGDIR_SHIFT determines what a third-level page table entry can map + */ +#define PMD_SHIFT 21 +#define PGDIR_SHIFT 21 + +#define PMD_SIZE (1UL << PMD_SHIFT) +#define PMD_MASK (~(PMD_SIZE-1)) +#define PGDIR_SIZE (1UL << PGDIR_SHIFT) +#define PGDIR_MASK (~(PGDIR_SIZE-1)) + +/* + * section address mask and size definitions. + */ +#define SECTION_SHIFT 20 +#define SECTION_SIZE (1UL << SECTION_SHIFT) +#define SECTION_MASK (~(SECTION_SIZE-1)) + +/* + * ARMv6 supersection address mask and size definitions. + */ +#define SUPERSECTION_SHIFT 24 +#define SUPERSECTION_SIZE (1UL << SUPERSECTION_SHIFT) +#define SUPERSECTION_MASK (~(SUPERSECTION_SIZE-1)) + +#define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE) + +/* + * "Linux" PTE definitions. + * + * We keep two sets of PTEs - the hardware and the linux version. + * This allows greater flexibility in the way we map the Linux bits + * onto the hardware tables, and allows us to have YOUNG and DIRTY + * bits. + * + * The PTE table pointer refers to the hardware entries; the "Linux" + * entries are stored 1024 bytes below. + */ +#define L_PTE_PRESENT (_AT(pteval_t, 1) << 0) +#define L_PTE_YOUNG (_AT(pteval_t, 1) << 1) +#define L_PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !PRESENT */ +#define L_PTE_DIRTY (_AT(pteval_t, 1) << 6) +#define L_PTE_RDONLY (_AT(pteval_t, 1) << 7) +#define L_PTE_USER (_AT(pteval_t, 1) << 8) +#define L_PTE_XN (_AT(pteval_t, 1) << 9) +#define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */ + +/* + * These are the memory types, defined to be compatible with + * pre-ARMv6 CPUs cacheable and bufferable bits: XXCB + */ +#define L_PTE_MT_UNCACHED (_AT(pteval_t, 0x00) << 2) /* 0000 */ +#define L_PTE_MT_BUFFERABLE (_AT(pteval_t, 0x01) << 2) /* 0001 */ +#define L_PTE_MT_WRITETHROUGH (_AT(pteval_t, 0x02) << 2) /* 0010 */ +#define L_PTE_MT_WRITEBACK (_AT(pteval_t, 0x03) << 2) /* 0011 */ +#define L_PTE_MT_MINICACHE (_AT(pteval_t, 0x06) << 2) /* 0110 (sa1100, xscale) */ +#define L_PTE_MT_WRITEALLOC (_AT(pteval_t, 0x07) << 2) /* 0111 */ +#define L_PTE_MT_DEV_SHARED (_AT(pteval_t, 0x04) << 2) /* 0100 */ +#define L_PTE_MT_DEV_NONSHARED (_AT(pteval_t, 0x0c) << 2) /* 1100 */ +#define L_PTE_MT_DEV_WC (_AT(pteval_t, 0x09) << 2) /* 1001 */ +#define L_PTE_MT_DEV_CACHED (_AT(pteval_t, 0x0b) << 2) /* 1011 */ +#define L_PTE_MT_MASK (_AT(pteval_t, 0x0f) << 2) + +#endif /* _ASM_PGTABLE_2LEVEL_H */ |