Release 4.14 arch/arc/mm/highmem.c
/*
* Copyright (C) 2015 Synopsys, Inc. (www.synopsys.com)
*
* 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.
*
*/
#include <linux/bootmem.h>
#include <linux/export.h>
#include <linux/highmem.h>
#include <asm/processor.h>
#include <asm/pgtable.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)
*
* - fixmap anyhow needs a limited number of mappings. So 2M kvaddr == 256 PTE
* slots across NR_CPUS would be more than sufficient (generic code defines
* KM_TYPE_NR as 20).
*
* - 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 pte_t * fixmap_page_table;
void *kmap(struct page *page)
{
BUG_ON(in_interrupt());
if (!PageHighMem(page))
return page_address(page);
return kmap_high(page);
}
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EXPORT_SYMBOL(kmap);
void *kmap_atomic(struct page *page)
{
int idx, cpu_idx;
unsigned long vaddr;
preempt_disable();
pagefault_disable();
if (!PageHighMem(page))
return page_address(page);
cpu_idx = kmap_atomic_idx_push();
idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
vaddr = FIXMAP_ADDR(idx);
set_pte_at(&init_mm, vaddr, fixmap_page_table + idx,
mk_pte(page, kmap_prot));
return (void *)vaddr;
}
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EXPORT_SYMBOL(kmap_atomic);
void __kunmap_atomic(void *kv)
{
unsigned long kvaddr = (unsigned long)kv;
if (kvaddr >= FIXMAP_BASE && kvaddr < (FIXMAP_BASE + FIXMAP_SIZE)) {
/*
* Because preemption is disabled, this vaddr can be associated
* with the current allocated index.
* But in case of multiple live kmap_atomic(), it still relies on
* callers to unmap in right order.
*/
int cpu_idx = kmap_atomic_idx();
int idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
WARN_ON(kvaddr != FIXMAP_ADDR(idx));
pte_clear(&init_mm, kvaddr, fixmap_page_table + idx);
local_flush_tlb_kernel_range(kvaddr, kvaddr + PAGE_SIZE);
kmap_atomic_idx_pop();
}
pagefault_enable();
preempt_enable();
}
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EXPORT_SYMBOL(__kunmap_atomic);
static noinline pte_t * __init alloc_kmap_pgtable(unsigned long kvaddr)
{
pgd_t *pgd_k;
pud_t *pud_k;
pmd_t *pmd_k;
pte_t *pte_k;
pgd_k = pgd_offset_k(kvaddr);
pud_k = pud_offset(pgd_k, kvaddr);
pmd_k = pmd_offset(pud_k, kvaddr);
pte_k = (pte_t *)alloc_bootmem_low_pages(PAGE_SIZE);
pmd_populate_kernel(&init_mm, pmd_k, pte_k);
return pte_k;
}
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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(KM_TYPE_NR > PTRS_PER_PTE);
pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE);
BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
fixmap_page_table = alloc_kmap_pgtable(FIXMAP_BASE);
}
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Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Vineet Gupta | 391 | 99.74% | 3 | 75.00% |
| Adam Buchbinder | 1 | 0.26% | 1 | 25.00% |
| Total | 392 | 100.00% | 4 | 100.00% |
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