350 lines
10 KiB
C
350 lines
10 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/pagewalk.h>
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#include <linux/hugetlb.h>
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#include <linux/bitops.h>
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#include <linux/mmu_notifier.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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/**
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* struct wp_walk - Private struct for pagetable walk callbacks
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* @range: Range for mmu notifiers
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* @tlbflush_start: Address of first modified pte
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* @tlbflush_end: Address of last modified pte + 1
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* @total: Total number of modified ptes
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*/
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struct wp_walk {
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struct mmu_notifier_range range;
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unsigned long tlbflush_start;
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unsigned long tlbflush_end;
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unsigned long total;
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};
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/**
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* wp_pte - Write-protect a pte
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* @pte: Pointer to the pte
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* @addr: The virtual page address
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* @walk: pagetable walk callback argument
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*
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* The function write-protects a pte and records the range in
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* virtual address space of touched ptes for efficient range TLB flushes.
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*/
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static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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struct wp_walk *wpwalk = walk->private;
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pte_t ptent = *pte;
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if (pte_write(ptent)) {
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pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
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ptent = pte_wrprotect(old_pte);
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ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
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wpwalk->total++;
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wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
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wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
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addr + PAGE_SIZE);
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}
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return 0;
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}
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/**
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* struct clean_walk - Private struct for the clean_record_pte function.
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* @base: struct wp_walk we derive from
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* @bitmap_pgoff: Address_space Page offset of the first bit in @bitmap
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* @bitmap: Bitmap with one bit for each page offset in the address_space range
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* covered.
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* @start: Address_space page offset of first modified pte relative
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* to @bitmap_pgoff
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* @end: Address_space page offset of last modified pte relative
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* to @bitmap_pgoff
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*/
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struct clean_walk {
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struct wp_walk base;
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pgoff_t bitmap_pgoff;
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unsigned long *bitmap;
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pgoff_t start;
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pgoff_t end;
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};
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#define to_clean_walk(_wpwalk) container_of(_wpwalk, struct clean_walk, base)
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/**
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* clean_record_pte - Clean a pte and record its address space offset in a
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* bitmap
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* @pte: Pointer to the pte
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* @addr: The virtual page address
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* @walk: pagetable walk callback argument
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*
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* The function cleans a pte and records the range in
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* virtual address space of touched ptes for efficient TLB flushes.
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* It also records dirty ptes in a bitmap representing page offsets
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* in the address_space, as well as the first and last of the bits
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* touched.
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*/
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static int clean_record_pte(pte_t *pte, unsigned long addr,
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unsigned long end, struct mm_walk *walk)
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{
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struct wp_walk *wpwalk = walk->private;
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struct clean_walk *cwalk = to_clean_walk(wpwalk);
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pte_t ptent = *pte;
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if (pte_dirty(ptent)) {
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pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) +
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walk->vma->vm_pgoff - cwalk->bitmap_pgoff;
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pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
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ptent = pte_mkclean(old_pte);
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ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
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wpwalk->total++;
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wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
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wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
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addr + PAGE_SIZE);
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__set_bit(pgoff, cwalk->bitmap);
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cwalk->start = min(cwalk->start, pgoff);
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cwalk->end = max(cwalk->end, pgoff + 1);
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}
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return 0;
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}
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/*
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* wp_clean_pmd_entry - The pagewalk pmd callback.
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*
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* Dirty-tracking should take place on the PTE level, so
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* WARN() if encountering a dirty huge pmd.
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* Furthermore, never split huge pmds, since that currently
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* causes dirty info loss. The pagefault handler should do
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* that if needed.
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*/
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static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pmd_t pmdval = pmd_read_atomic(pmd);
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if (!pmd_trans_unstable(&pmdval))
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return 0;
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if (pmd_none(pmdval)) {
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walk->action = ACTION_AGAIN;
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return 0;
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}
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/* Huge pmd, present or migrated */
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walk->action = ACTION_CONTINUE;
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if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
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WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
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return 0;
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}
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/*
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* wp_clean_pud_entry - The pagewalk pud callback.
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*
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* Dirty-tracking should take place on the PTE level, so
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* WARN() if encountering a dirty huge puds.
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* Furthermore, never split huge puds, since that currently
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* causes dirty info loss. The pagefault handler should do
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* that if needed.
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*/
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static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pud_t pudval = READ_ONCE(*pud);
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if (!pud_trans_unstable(&pudval))
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return 0;
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if (pud_none(pudval)) {
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walk->action = ACTION_AGAIN;
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return 0;
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}
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/* Huge pud */
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walk->action = ACTION_CONTINUE;
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if (pud_trans_huge(pudval) || pud_devmap(pudval))
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WARN_ON(pud_write(pudval) || pud_dirty(pudval));
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return 0;
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}
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/*
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* wp_clean_pre_vma - The pagewalk pre_vma callback.
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*
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* The pre_vma callback performs the cache flush, stages the tlb flush
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* and calls the necessary mmu notifiers.
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*/
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static int wp_clean_pre_vma(unsigned long start, unsigned long end,
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struct mm_walk *walk)
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{
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struct wp_walk *wpwalk = walk->private;
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wpwalk->tlbflush_start = end;
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wpwalk->tlbflush_end = start;
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mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
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walk->vma, walk->mm, start, end);
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mmu_notifier_invalidate_range_start(&wpwalk->range);
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flush_cache_range(walk->vma, start, end);
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/*
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* We're not using tlb_gather_mmu() since typically
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* only a small subrange of PTEs are affected, whereas
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* tlb_gather_mmu() records the full range.
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*/
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inc_tlb_flush_pending(walk->mm);
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return 0;
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}
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/*
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* wp_clean_post_vma - The pagewalk post_vma callback.
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*
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* The post_vma callback performs the tlb flush and calls necessary mmu
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* notifiers.
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*/
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static void wp_clean_post_vma(struct mm_walk *walk)
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{
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struct wp_walk *wpwalk = walk->private;
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if (mm_tlb_flush_nested(walk->mm))
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flush_tlb_range(walk->vma, wpwalk->range.start,
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wpwalk->range.end);
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else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
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flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
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wpwalk->tlbflush_end);
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mmu_notifier_invalidate_range_end(&wpwalk->range);
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dec_tlb_flush_pending(walk->mm);
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}
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/*
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* wp_clean_test_walk - The pagewalk test_walk callback.
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*
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* Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
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*/
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static int wp_clean_test_walk(unsigned long start, unsigned long end,
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struct mm_walk *walk)
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{
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unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);
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/* Skip non-applicable VMAs */
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if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
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(VM_SHARED | VM_MAYWRITE))
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return 1;
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return 0;
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}
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static const struct mm_walk_ops clean_walk_ops = {
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.pte_entry = clean_record_pte,
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.pmd_entry = wp_clean_pmd_entry,
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.pud_entry = wp_clean_pud_entry,
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.test_walk = wp_clean_test_walk,
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.pre_vma = wp_clean_pre_vma,
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.post_vma = wp_clean_post_vma
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};
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static const struct mm_walk_ops wp_walk_ops = {
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.pte_entry = wp_pte,
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.pmd_entry = wp_clean_pmd_entry,
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.pud_entry = wp_clean_pud_entry,
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.test_walk = wp_clean_test_walk,
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.pre_vma = wp_clean_pre_vma,
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.post_vma = wp_clean_post_vma
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};
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/**
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* wp_shared_mapping_range - Write-protect all ptes in an address space range
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* @mapping: The address_space we want to write protect
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* @first_index: The first page offset in the range
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* @nr: Number of incremental page offsets to cover
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*
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* Note: This function currently skips transhuge page-table entries, since
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* it's intended for dirty-tracking on the PTE level. It will warn on
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* encountering transhuge write-enabled entries, though, and can easily be
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* extended to handle them as well.
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*
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* Return: The number of ptes actually write-protected. Note that
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* already write-protected ptes are not counted.
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*/
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unsigned long wp_shared_mapping_range(struct address_space *mapping,
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pgoff_t first_index, pgoff_t nr)
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{
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struct wp_walk wpwalk = { .total = 0 };
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i_mmap_lock_read(mapping);
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WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
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&wpwalk));
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i_mmap_unlock_read(mapping);
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return wpwalk.total;
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}
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EXPORT_SYMBOL_GPL(wp_shared_mapping_range);
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/**
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* clean_record_shared_mapping_range - Clean and record all ptes in an
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* address space range
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* @mapping: The address_space we want to clean
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* @first_index: The first page offset in the range
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* @nr: Number of incremental page offsets to cover
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* @bitmap_pgoff: The page offset of the first bit in @bitmap
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* @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
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* cover the whole range @first_index..@first_index + @nr.
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* @start: Pointer to number of the first set bit in @bitmap.
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* is modified as new bits are set by the function.
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* @end: Pointer to the number of the last set bit in @bitmap.
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* none set. The value is modified as new bits are set by the function.
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*
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* Note: When this function returns there is no guarantee that a CPU has
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* not already dirtied new ptes. However it will not clean any ptes not
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* reported in the bitmap. The guarantees are as follows:
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* a) All ptes dirty when the function starts executing will end up recorded
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* in the bitmap.
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* b) All ptes dirtied after that will either remain dirty, be recorded in the
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* bitmap or both.
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*
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* If a caller needs to make sure all dirty ptes are picked up and none
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* additional are added, it first needs to write-protect the address-space
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* range and make sure new writers are blocked in page_mkwrite() or
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* pfn_mkwrite(). And then after a TLB flush following the write-protection
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* pick up all dirty bits.
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*
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* Note: This function currently skips transhuge page-table entries, since
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* it's intended for dirty-tracking on the PTE level. It will warn on
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* encountering transhuge dirty entries, though, and can easily be extended
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* to handle them as well.
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*
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* Return: The number of dirty ptes actually cleaned.
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*/
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unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
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pgoff_t first_index, pgoff_t nr,
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pgoff_t bitmap_pgoff,
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unsigned long *bitmap,
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pgoff_t *start,
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pgoff_t *end)
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{
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bool none_set = (*start >= *end);
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struct clean_walk cwalk = {
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.base = { .total = 0 },
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.bitmap_pgoff = bitmap_pgoff,
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.bitmap = bitmap,
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.start = none_set ? nr : *start,
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.end = none_set ? 0 : *end,
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};
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i_mmap_lock_read(mapping);
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WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
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&cwalk.base));
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i_mmap_unlock_read(mapping);
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*start = cwalk.start;
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*end = cwalk.end;
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return cwalk.base.total;
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}
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EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);
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