blob: c79912a6b19615bbb5235fe5868df157ade2df3b [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
* Copyright (C) 2015 Synopsys, Inc. (
#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>
* 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
* - 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 */
pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE);