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![Steve Capper](/assets/img/avatar_default.png)
For contiguous hugetlb, huge_ptep_set_access_flags performs a
get_clear_flush (which then flushes the TLBs) even when no change of ptes
is necessary.
Unfortunately, this behaviour can lead to back-to-back page faults being
generated when running with multiple threads that access the same
contiguous huge page.
Thread 1 | Thread 2
-----------------------------+------------------------------
hugetlb_fault |
huge_ptep_set_access_flags |
-> invalidate pte range | hugetlb_fault
continue processing | wait for hugetlb_fault_mutex
release mutex and return | huge_ptep_set_access_flags
| -> invalidate pte range
hugetlb_fault
...
This patch changes huge_ptep_set_access_flags s.t. we first read the
contiguous range of ptes (whilst preserving dirty information); the pte
range is only then invalidated where necessary and this prevents further
spurious page faults.
Fixes: d8bdcff287
("arm64: hugetlb: Add break-before-make logic for contiguous entries")
Reported-by: Lei Zhang <zhang.lei@jp.fujitsu.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
461 lines
11 KiB
C
461 lines
11 KiB
C
/*
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* arch/arm64/mm/hugetlbpage.c
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*
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* Copyright (C) 2013 Linaro Ltd.
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*
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* Based on arch/x86/mm/hugetlbpage.c.
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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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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/mm.h>
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#include <linux/hugetlb.h>
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#include <linux/pagemap.h>
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#include <linux/err.h>
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#include <linux/sysctl.h>
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#include <asm/mman.h>
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#include <asm/tlb.h>
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#include <asm/tlbflush.h>
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#include <asm/pgalloc.h>
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int pmd_huge(pmd_t pmd)
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{
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return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
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}
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int pud_huge(pud_t pud)
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{
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#ifndef __PAGETABLE_PMD_FOLDED
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return pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT);
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#else
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return 0;
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#endif
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}
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/*
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* Select all bits except the pfn
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*/
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static inline pgprot_t pte_pgprot(pte_t pte)
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{
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unsigned long pfn = pte_pfn(pte);
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return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
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}
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static int find_num_contig(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, size_t *pgsize)
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{
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pgd_t *pgdp = pgd_offset(mm, addr);
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pud_t *pudp;
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pmd_t *pmdp;
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*pgsize = PAGE_SIZE;
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pudp = pud_offset(pgdp, addr);
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pmdp = pmd_offset(pudp, addr);
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if ((pte_t *)pmdp == ptep) {
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*pgsize = PMD_SIZE;
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return CONT_PMDS;
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}
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return CONT_PTES;
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}
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static inline int num_contig_ptes(unsigned long size, size_t *pgsize)
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{
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int contig_ptes = 0;
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*pgsize = size;
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switch (size) {
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#ifdef CONFIG_ARM64_4K_PAGES
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case PUD_SIZE:
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#endif
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case PMD_SIZE:
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contig_ptes = 1;
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break;
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case CONT_PMD_SIZE:
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*pgsize = PMD_SIZE;
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contig_ptes = CONT_PMDS;
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break;
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case CONT_PTE_SIZE:
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*pgsize = PAGE_SIZE;
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contig_ptes = CONT_PTES;
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break;
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}
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return contig_ptes;
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}
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/*
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* Changing some bits of contiguous entries requires us to follow a
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* Break-Before-Make approach, breaking the whole contiguous set
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* before we can change any entries. See ARM DDI 0487A.k_iss10775,
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* "Misprogramming of the Contiguous bit", page D4-1762.
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*
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* This helper performs the break step.
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*/
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static pte_t get_clear_flush(struct mm_struct *mm,
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unsigned long addr,
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pte_t *ptep,
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unsigned long pgsize,
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unsigned long ncontig)
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{
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pte_t orig_pte = huge_ptep_get(ptep);
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bool valid = pte_valid(orig_pte);
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unsigned long i, saddr = addr;
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for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
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pte_t pte = ptep_get_and_clear(mm, addr, ptep);
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/*
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* If HW_AFDBM is enabled, then the HW could turn on
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* the dirty or accessed bit for any page in the set,
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* so check them all.
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*/
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if (pte_dirty(pte))
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orig_pte = pte_mkdirty(orig_pte);
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if (pte_young(pte))
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orig_pte = pte_mkyoung(orig_pte);
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}
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if (valid) {
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struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0);
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flush_tlb_range(&vma, saddr, addr);
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}
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return orig_pte;
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}
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/*
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* Changing some bits of contiguous entries requires us to follow a
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* Break-Before-Make approach, breaking the whole contiguous set
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* before we can change any entries. See ARM DDI 0487A.k_iss10775,
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* "Misprogramming of the Contiguous bit", page D4-1762.
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*
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* This helper performs the break step for use cases where the
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* original pte is not needed.
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*/
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static void clear_flush(struct mm_struct *mm,
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unsigned long addr,
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pte_t *ptep,
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unsigned long pgsize,
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unsigned long ncontig)
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{
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struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0);
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unsigned long i, saddr = addr;
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for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
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pte_clear(mm, addr, ptep);
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flush_tlb_range(&vma, saddr, addr);
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}
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void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, pte_t pte)
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{
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size_t pgsize;
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int i;
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int ncontig;
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unsigned long pfn, dpfn;
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pgprot_t hugeprot;
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/*
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* Code needs to be expanded to handle huge swap and migration
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* entries. Needed for HUGETLB and MEMORY_FAILURE.
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*/
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WARN_ON(!pte_present(pte));
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if (!pte_cont(pte)) {
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set_pte_at(mm, addr, ptep, pte);
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return;
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}
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ncontig = find_num_contig(mm, addr, ptep, &pgsize);
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pfn = pte_pfn(pte);
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dpfn = pgsize >> PAGE_SHIFT;
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hugeprot = pte_pgprot(pte);
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clear_flush(mm, addr, ptep, pgsize, ncontig);
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for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
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set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
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}
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void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, pte_t pte, unsigned long sz)
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{
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int i, ncontig;
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size_t pgsize;
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ncontig = num_contig_ptes(sz, &pgsize);
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for (i = 0; i < ncontig; i++, ptep++)
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set_pte(ptep, pte);
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}
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pte_t *huge_pte_alloc(struct mm_struct *mm,
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unsigned long addr, unsigned long sz)
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{
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pgd_t *pgdp;
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pud_t *pudp;
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pmd_t *pmdp;
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pte_t *ptep = NULL;
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pgdp = pgd_offset(mm, addr);
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pudp = pud_alloc(mm, pgdp, addr);
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if (!pudp)
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return NULL;
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if (sz == PUD_SIZE) {
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ptep = (pte_t *)pudp;
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} else if (sz == (PAGE_SIZE * CONT_PTES)) {
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pmdp = pmd_alloc(mm, pudp, addr);
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WARN_ON(addr & (sz - 1));
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/*
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* Note that if this code were ever ported to the
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* 32-bit arm platform then it will cause trouble in
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* the case where CONFIG_HIGHPTE is set, since there
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* will be no pte_unmap() to correspond with this
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* pte_alloc_map().
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*/
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ptep = pte_alloc_map(mm, pmdp, addr);
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} else if (sz == PMD_SIZE) {
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if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) &&
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pud_none(READ_ONCE(*pudp)))
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ptep = huge_pmd_share(mm, addr, pudp);
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else
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ptep = (pte_t *)pmd_alloc(mm, pudp, addr);
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} else if (sz == (PMD_SIZE * CONT_PMDS)) {
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pmdp = pmd_alloc(mm, pudp, addr);
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WARN_ON(addr & (sz - 1));
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return (pte_t *)pmdp;
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}
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return ptep;
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}
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pte_t *huge_pte_offset(struct mm_struct *mm,
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unsigned long addr, unsigned long sz)
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{
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pgd_t *pgdp;
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pud_t *pudp, pud;
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pmd_t *pmdp, pmd;
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pgdp = pgd_offset(mm, addr);
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if (!pgd_present(READ_ONCE(*pgdp)))
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return NULL;
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pudp = pud_offset(pgdp, addr);
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pud = READ_ONCE(*pudp);
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if (sz != PUD_SIZE && pud_none(pud))
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return NULL;
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/* hugepage or swap? */
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if (pud_huge(pud) || !pud_present(pud))
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return (pte_t *)pudp;
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/* table; check the next level */
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if (sz == CONT_PMD_SIZE)
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addr &= CONT_PMD_MASK;
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pmdp = pmd_offset(pudp, addr);
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pmd = READ_ONCE(*pmdp);
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if (!(sz == PMD_SIZE || sz == CONT_PMD_SIZE) &&
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pmd_none(pmd))
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return NULL;
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if (pmd_huge(pmd) || !pmd_present(pmd))
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return (pte_t *)pmdp;
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if (sz == CONT_PTE_SIZE)
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return pte_offset_kernel(pmdp, (addr & CONT_PTE_MASK));
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return NULL;
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}
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pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
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struct page *page, int writable)
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{
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size_t pagesize = huge_page_size(hstate_vma(vma));
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if (pagesize == CONT_PTE_SIZE) {
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entry = pte_mkcont(entry);
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} else if (pagesize == CONT_PMD_SIZE) {
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entry = pmd_pte(pmd_mkcont(pte_pmd(entry)));
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} else if (pagesize != PUD_SIZE && pagesize != PMD_SIZE) {
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pr_warn("%s: unrecognized huge page size 0x%lx\n",
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__func__, pagesize);
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}
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return entry;
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}
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void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, unsigned long sz)
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{
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int i, ncontig;
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size_t pgsize;
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ncontig = num_contig_ptes(sz, &pgsize);
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for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
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pte_clear(mm, addr, ptep);
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}
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pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
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unsigned long addr, pte_t *ptep)
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{
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int ncontig;
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size_t pgsize;
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pte_t orig_pte = huge_ptep_get(ptep);
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if (!pte_cont(orig_pte))
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return ptep_get_and_clear(mm, addr, ptep);
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ncontig = find_num_contig(mm, addr, ptep, &pgsize);
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return get_clear_flush(mm, addr, ptep, pgsize, ncontig);
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}
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/*
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* huge_ptep_set_access_flags will update access flags (dirty, accesssed)
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* and write permission.
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*
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* For a contiguous huge pte range we need to check whether or not write
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* permission has to change only on the first pte in the set. Then for
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* all the contiguous ptes we need to check whether or not there is a
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* discrepancy between dirty or young.
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*/
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static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig)
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{
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int i;
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if (pte_write(pte) != pte_write(huge_ptep_get(ptep)))
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return 1;
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for (i = 0; i < ncontig; i++) {
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pte_t orig_pte = huge_ptep_get(ptep + i);
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if (pte_dirty(pte) != pte_dirty(orig_pte))
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return 1;
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if (pte_young(pte) != pte_young(orig_pte))
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return 1;
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}
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return 0;
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}
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int huge_ptep_set_access_flags(struct vm_area_struct *vma,
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unsigned long addr, pte_t *ptep,
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pte_t pte, int dirty)
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{
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int ncontig, i;
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size_t pgsize = 0;
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unsigned long pfn = pte_pfn(pte), dpfn;
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pgprot_t hugeprot;
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pte_t orig_pte;
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if (!pte_cont(pte))
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return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
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ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
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dpfn = pgsize >> PAGE_SHIFT;
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if (!__cont_access_flags_changed(ptep, pte, ncontig))
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return 0;
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orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
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/* Make sure we don't lose the dirty or young state */
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if (pte_dirty(orig_pte))
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pte = pte_mkdirty(pte);
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if (pte_young(orig_pte))
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pte = pte_mkyoung(pte);
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hugeprot = pte_pgprot(pte);
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for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
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set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot));
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return 1;
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}
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void huge_ptep_set_wrprotect(struct mm_struct *mm,
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unsigned long addr, pte_t *ptep)
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{
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unsigned long pfn, dpfn;
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pgprot_t hugeprot;
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int ncontig, i;
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size_t pgsize;
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pte_t pte;
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if (!pte_cont(READ_ONCE(*ptep))) {
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ptep_set_wrprotect(mm, addr, ptep);
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return;
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}
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ncontig = find_num_contig(mm, addr, ptep, &pgsize);
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dpfn = pgsize >> PAGE_SHIFT;
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pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);
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pte = pte_wrprotect(pte);
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hugeprot = pte_pgprot(pte);
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pfn = pte_pfn(pte);
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for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
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set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
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}
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void huge_ptep_clear_flush(struct vm_area_struct *vma,
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unsigned long addr, pte_t *ptep)
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{
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size_t pgsize;
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int ncontig;
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if (!pte_cont(READ_ONCE(*ptep))) {
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ptep_clear_flush(vma, addr, ptep);
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return;
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}
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ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
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clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
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}
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static __init int setup_hugepagesz(char *opt)
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{
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unsigned long ps = memparse(opt, &opt);
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switch (ps) {
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#ifdef CONFIG_ARM64_4K_PAGES
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case PUD_SIZE:
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#endif
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case PMD_SIZE * CONT_PMDS:
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case PMD_SIZE:
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case PAGE_SIZE * CONT_PTES:
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hugetlb_add_hstate(ilog2(ps) - PAGE_SHIFT);
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return 1;
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}
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hugetlb_bad_size();
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pr_err("hugepagesz: Unsupported page size %lu K\n", ps >> 10);
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return 0;
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}
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__setup("hugepagesz=", setup_hugepagesz);
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#ifdef CONFIG_ARM64_64K_PAGES
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static __init int add_default_hugepagesz(void)
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{
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if (size_to_hstate(CONT_PTES * PAGE_SIZE) == NULL)
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hugetlb_add_hstate(CONT_PTE_SHIFT);
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return 0;
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}
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arch_initcall(add_default_hugepagesz);
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#endif
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