142 lines
4 KiB
C
142 lines
4 KiB
C
/*
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* Copyright (C) 2015 Synopsys, Inc. (www.synopsys.com)
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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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*/
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#include <linux/bootmem.h>
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#include <linux/export.h>
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#include <linux/highmem.h>
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#include <asm/processor.h>
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#include <asm/pgtable.h>
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#include <asm/pgalloc.h>
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#include <asm/tlbflush.h>
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/*
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* HIGHMEM API:
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*
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* kmap() API provides sleep semantics hence referred to as "permanent maps"
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* It allows mapping LAST_PKMAP pages, using @last_pkmap_nr as the cursor
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* for book-keeping
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*
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* kmap_atomic() can't sleep (calls pagefault_disable()), thus it provides
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* shortlived ala "temporary mappings" which historically were implemented as
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* fixmaps (compile time addr etc). Their book-keeping is done per cpu.
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*
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* Both these facts combined (preemption disabled and per-cpu allocation)
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* means the total number of concurrent fixmaps will be limited to max
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* such allocations in a single control path. Thus KM_TYPE_NR (another
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* historic relic) is a small'ish number which caps max percpu fixmaps
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*
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* ARC HIGHMEM Details
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*
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* - the kernel vaddr space from 0x7z to 0x8z (currently used by vmalloc/module)
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* is now shared between vmalloc and kmap (non overlapping though)
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*
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* - Both fixmap/pkmap use a dedicated page table each, hooked up to swapper PGD
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* This means each only has 1 PGDIR_SIZE worth of kvaddr mappings, which means
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* 2M of kvaddr space for typical config (8K page and 11:8:13 traversal split)
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*
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* - fixmap anyhow needs a limited number of mappings. So 2M kvaddr == 256 PTE
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* slots across NR_CPUS would be more than sufficient (generic code defines
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* KM_TYPE_NR as 20).
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*
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* - pkmap being preemptible, in theory could do with more than 256 concurrent
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* mappings. However, generic pkmap code: map_new_virtual(), doesn't traverse
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* the PGD and only works with a single page table @pkmap_page_table, hence
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* sets the limit
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*/
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extern pte_t * pkmap_page_table;
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static pte_t * fixmap_page_table;
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void *kmap(struct page *page)
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{
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BUG_ON(in_interrupt());
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if (!PageHighMem(page))
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return page_address(page);
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return kmap_high(page);
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}
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EXPORT_SYMBOL(kmap);
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void *kmap_atomic(struct page *page)
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{
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int idx, cpu_idx;
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unsigned long vaddr;
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preempt_disable();
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pagefault_disable();
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if (!PageHighMem(page))
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return page_address(page);
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cpu_idx = kmap_atomic_idx_push();
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idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
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vaddr = FIXMAP_ADDR(idx);
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set_pte_at(&init_mm, vaddr, fixmap_page_table + idx,
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mk_pte(page, kmap_prot));
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return (void *)vaddr;
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}
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EXPORT_SYMBOL(kmap_atomic);
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void __kunmap_atomic(void *kv)
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{
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unsigned long kvaddr = (unsigned long)kv;
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if (kvaddr >= FIXMAP_BASE && kvaddr < (FIXMAP_BASE + FIXMAP_SIZE)) {
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/*
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* Because preemption is disabled, this vaddr can be associated
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* with the current allocated index.
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* But in case of multiple live kmap_atomic(), it still relies on
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* callers to unmap in right order.
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*/
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int cpu_idx = kmap_atomic_idx();
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int idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
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WARN_ON(kvaddr != FIXMAP_ADDR(idx));
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pte_clear(&init_mm, kvaddr, fixmap_page_table + idx);
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local_flush_tlb_kernel_range(kvaddr, kvaddr + PAGE_SIZE);
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kmap_atomic_idx_pop();
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}
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pagefault_enable();
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preempt_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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static noinline pte_t * __init alloc_kmap_pgtable(unsigned long kvaddr)
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{
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pgd_t *pgd_k;
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pud_t *pud_k;
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pmd_t *pmd_k;
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pte_t *pte_k;
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pgd_k = pgd_offset_k(kvaddr);
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pud_k = pud_offset(pgd_k, kvaddr);
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pmd_k = pmd_offset(pud_k, kvaddr);
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pte_k = (pte_t *)alloc_bootmem_low_pages(PAGE_SIZE);
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pmd_populate_kernel(&init_mm, pmd_k, pte_k);
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return pte_k;
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}
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void __init kmap_init(void)
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{
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/* Due to recursive include hell, we can't do this in processor.h */
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BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
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BUILD_BUG_ON(KM_TYPE_NR > PTRS_PER_PTE);
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pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE);
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BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
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fixmap_page_table = alloc_kmap_pgtable(FIXMAP_BASE);
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}
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