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Diffstat (limited to 'arch/arc/mm/highmem.c')
| -rw-r--r-- | arch/arc/mm/highmem.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/arch/arc/mm/highmem.c b/arch/arc/mm/highmem.c new file mode 100644 index 000000000..c79912a6b --- /dev/null +++ b/arch/arc/mm/highmem.c @@ -0,0 +1,73 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2015 Synopsys, Inc. (www.synopsys.com) + */ + +#include <linux/memblock.h> +#include <linux/export.h> +#include <linux/highmem.h> +#include <linux/pgtable.h> +#include <asm/processor.h> +#include <asm/pgalloc.h> +#include <asm/tlbflush.h> + +/* + * HIGHMEM API: + * + * kmap() API provides sleep semantics hence referred to as "permanent maps" + * It allows mapping LAST_PKMAP pages, using @last_pkmap_nr as the cursor + * for book-keeping + * + * kmap_atomic() can't sleep (calls pagefault_disable()), thus it provides + * shortlived ala "temporary mappings" which historically were implemented as + * fixmaps (compile time addr etc). Their book-keeping is done per cpu. + * + * Both these facts combined (preemption disabled and per-cpu allocation) + * means the total number of concurrent fixmaps will be limited to max + * such allocations in a single control path. Thus KM_TYPE_NR (another + * historic relic) is a small'ish number which caps max percpu fixmaps + * + * ARC HIGHMEM Details + * + * - the kernel vaddr space from 0x7z to 0x8z (currently used by vmalloc/module) + * is now shared between vmalloc and kmap (non overlapping though) + * + * - Both fixmap/pkmap use a dedicated page table each, hooked up to swapper PGD + * This means each only has 1 PGDIR_SIZE worth of kvaddr mappings, which means + * 2M of kvaddr space for typical config (8K page and 11:8:13 traversal split) + * + * - The fixed KMAP slots for kmap_local/atomic() require KM_MAX_IDX slots per + * CPU. So the number of CPUs sharing a single PTE page is limited. + * + * - pkmap being preemptible, in theory could do with more than 256 concurrent + * mappings. However, generic pkmap code: map_new_virtual(), doesn't traverse + * the PGD and only works with a single page table @pkmap_page_table, hence + * sets the limit + */ + +extern pte_t * pkmap_page_table; + +static noinline pte_t * __init alloc_kmap_pgtable(unsigned long kvaddr) +{ + pmd_t *pmd_k = pmd_off_k(kvaddr); + pte_t *pte_k; + + pte_k = (pte_t *)memblock_alloc_low(PAGE_SIZE, PAGE_SIZE); + if (!pte_k) + panic("%s: Failed to allocate %lu bytes align=0x%lx\n", + __func__, PAGE_SIZE, PAGE_SIZE); + + pmd_populate_kernel(&init_mm, pmd_k, pte_k); + return pte_k; +} + +void __init kmap_init(void) +{ + /* Due to recursive include hell, we can't do this in processor.h */ + BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE)); + BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE); + BUILD_BUG_ON(FIX_KMAP_SLOTS > PTRS_PER_PTE); + + pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE); + alloc_kmap_pgtable(FIXMAP_BASE); +} |