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Diffstat (limited to '')
| -rw-r--r-- | mm/mapping_dirty_helpers.c | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c new file mode 100644 index 000000000..2c7d03675 --- /dev/null +++ b/mm/mapping_dirty_helpers.c @@ -0,0 +1,349 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/pagewalk.h> +#include <linux/hugetlb.h> +#include <linux/bitops.h> +#include <linux/mmu_notifier.h> +#include <asm/cacheflush.h> +#include <asm/tlbflush.h> + +/** + * struct wp_walk - Private struct for pagetable walk callbacks + * @range: Range for mmu notifiers + * @tlbflush_start: Address of first modified pte + * @tlbflush_end: Address of last modified pte + 1 + * @total: Total number of modified ptes + */ +struct wp_walk { + struct mmu_notifier_range range; + unsigned long tlbflush_start; + unsigned long tlbflush_end; + unsigned long total; +}; + +/** + * wp_pte - Write-protect a pte + * @pte: Pointer to the pte + * @addr: The virtual page address + * @walk: pagetable walk callback argument + * + * The function write-protects a pte and records the range in + * virtual address space of touched ptes for efficient range TLB flushes. + */ +static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + struct wp_walk *wpwalk = walk->private; + pte_t ptent = *pte; + + if (pte_write(ptent)) { + pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte); + + ptent = pte_wrprotect(old_pte); + ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent); + wpwalk->total++; + wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr); + wpwalk->tlbflush_end = max(wpwalk->tlbflush_end, + addr + PAGE_SIZE); + } + + return 0; +} + +/** + * struct clean_walk - Private struct for the clean_record_pte function. + * @base: struct wp_walk we derive from + * @bitmap_pgoff: Address_space Page offset of the first bit in @bitmap + * @bitmap: Bitmap with one bit for each page offset in the address_space range + * covered. + * @start: Address_space page offset of first modified pte relative + * to @bitmap_pgoff + * @end: Address_space page offset of last modified pte relative + * to @bitmap_pgoff + */ +struct clean_walk { + struct wp_walk base; + pgoff_t bitmap_pgoff; + unsigned long *bitmap; + pgoff_t start; + pgoff_t end; +}; + +#define to_clean_walk(_wpwalk) container_of(_wpwalk, struct clean_walk, base) + +/** + * clean_record_pte - Clean a pte and record its address space offset in a + * bitmap + * @pte: Pointer to the pte + * @addr: The virtual page address + * @walk: pagetable walk callback argument + * + * The function cleans a pte and records the range in + * virtual address space of touched ptes for efficient TLB flushes. + * It also records dirty ptes in a bitmap representing page offsets + * in the address_space, as well as the first and last of the bits + * touched. + */ +static int clean_record_pte(pte_t *pte, unsigned long addr, + unsigned long end, struct mm_walk *walk) +{ + struct wp_walk *wpwalk = walk->private; + struct clean_walk *cwalk = to_clean_walk(wpwalk); + pte_t ptent = *pte; + + if (pte_dirty(ptent)) { + pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) + + walk->vma->vm_pgoff - cwalk->bitmap_pgoff; + pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte); + + ptent = pte_mkclean(old_pte); + ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent); + + wpwalk->total++; + wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr); + wpwalk->tlbflush_end = max(wpwalk->tlbflush_end, + addr + PAGE_SIZE); + + __set_bit(pgoff, cwalk->bitmap); + cwalk->start = min(cwalk->start, pgoff); + cwalk->end = max(cwalk->end, pgoff + 1); + } + + return 0; +} + +/* + * wp_clean_pmd_entry - The pagewalk pmd callback. + * + * Dirty-tracking should take place on the PTE level, so + * WARN() if encountering a dirty huge pmd. + * Furthermore, never split huge pmds, since that currently + * causes dirty info loss. The pagefault handler should do + * that if needed. + */ +static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pmd_t pmdval = pmd_read_atomic(pmd); + + if (!pmd_trans_unstable(&pmdval)) + return 0; + + if (pmd_none(pmdval)) { + walk->action = ACTION_AGAIN; + return 0; + } + + /* Huge pmd, present or migrated */ + walk->action = ACTION_CONTINUE; + if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval)) + WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval)); + + return 0; +} + +/* + * wp_clean_pud_entry - The pagewalk pud callback. + * + * Dirty-tracking should take place on the PTE level, so + * WARN() if encountering a dirty huge puds. + * Furthermore, never split huge puds, since that currently + * causes dirty info loss. The pagefault handler should do + * that if needed. + */ +static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pud_t pudval = READ_ONCE(*pud); + + if (!pud_trans_unstable(&pudval)) + return 0; + + if (pud_none(pudval)) { + walk->action = ACTION_AGAIN; + return 0; + } + + /* Huge pud */ + walk->action = ACTION_CONTINUE; + if (pud_trans_huge(pudval) || pud_devmap(pudval)) + WARN_ON(pud_write(pudval) || pud_dirty(pudval)); + + return 0; +} + +/* + * wp_clean_pre_vma - The pagewalk pre_vma callback. + * + * The pre_vma callback performs the cache flush, stages the tlb flush + * and calls the necessary mmu notifiers. + */ +static int wp_clean_pre_vma(unsigned long start, unsigned long end, + struct mm_walk *walk) +{ + struct wp_walk *wpwalk = walk->private; + + wpwalk->tlbflush_start = end; + wpwalk->tlbflush_end = start; + + mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0, + walk->vma, walk->mm, start, end); + mmu_notifier_invalidate_range_start(&wpwalk->range); + flush_cache_range(walk->vma, start, end); + + /* + * We're not using tlb_gather_mmu() since typically + * only a small subrange of PTEs are affected, whereas + * tlb_gather_mmu() records the full range. + */ + inc_tlb_flush_pending(walk->mm); + + return 0; +} + +/* + * wp_clean_post_vma - The pagewalk post_vma callback. + * + * The post_vma callback performs the tlb flush and calls necessary mmu + * notifiers. + */ +static void wp_clean_post_vma(struct mm_walk *walk) +{ + struct wp_walk *wpwalk = walk->private; + + if (mm_tlb_flush_nested(walk->mm)) + flush_tlb_range(walk->vma, wpwalk->range.start, + wpwalk->range.end); + else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start) + flush_tlb_range(walk->vma, wpwalk->tlbflush_start, + wpwalk->tlbflush_end); + + mmu_notifier_invalidate_range_end(&wpwalk->range); + dec_tlb_flush_pending(walk->mm); +} + +/* + * wp_clean_test_walk - The pagewalk test_walk callback. + * + * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas. + */ +static int wp_clean_test_walk(unsigned long start, unsigned long end, + struct mm_walk *walk) +{ + unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags); + + /* Skip non-applicable VMAs */ + if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) != + (VM_SHARED | VM_MAYWRITE)) + return 1; + + return 0; +} + +static const struct mm_walk_ops clean_walk_ops = { + .pte_entry = clean_record_pte, + .pmd_entry = wp_clean_pmd_entry, + .pud_entry = wp_clean_pud_entry, + .test_walk = wp_clean_test_walk, + .pre_vma = wp_clean_pre_vma, + .post_vma = wp_clean_post_vma +}; + +static const struct mm_walk_ops wp_walk_ops = { + .pte_entry = wp_pte, + .pmd_entry = wp_clean_pmd_entry, + .pud_entry = wp_clean_pud_entry, + .test_walk = wp_clean_test_walk, + .pre_vma = wp_clean_pre_vma, + .post_vma = wp_clean_post_vma +}; + +/** + * wp_shared_mapping_range - Write-protect all ptes in an address space range + * @mapping: The address_space we want to write protect + * @first_index: The first page offset in the range + * @nr: Number of incremental page offsets to cover + * + * Note: This function currently skips transhuge page-table entries, since + * it's intended for dirty-tracking on the PTE level. It will warn on + * encountering transhuge write-enabled entries, though, and can easily be + * extended to handle them as well. + * + * Return: The number of ptes actually write-protected. Note that + * already write-protected ptes are not counted. + */ +unsigned long wp_shared_mapping_range(struct address_space *mapping, + pgoff_t first_index, pgoff_t nr) +{ + struct wp_walk wpwalk = { .total = 0 }; + + i_mmap_lock_read(mapping); + WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops, + &wpwalk)); + i_mmap_unlock_read(mapping); + + return wpwalk.total; +} +EXPORT_SYMBOL_GPL(wp_shared_mapping_range); + +/** + * clean_record_shared_mapping_range - Clean and record all ptes in an + * address space range + * @mapping: The address_space we want to clean + * @first_index: The first page offset in the range + * @nr: Number of incremental page offsets to cover + * @bitmap_pgoff: The page offset of the first bit in @bitmap + * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to + * cover the whole range @first_index..@first_index + @nr. + * @start: Pointer to number of the first set bit in @bitmap. + * is modified as new bits are set by the function. + * @end: Pointer to the number of the last set bit in @bitmap. + * none set. The value is modified as new bits are set by the function. + * + * Note: When this function returns there is no guarantee that a CPU has + * not already dirtied new ptes. However it will not clean any ptes not + * reported in the bitmap. The guarantees are as follows: + * a) All ptes dirty when the function starts executing will end up recorded + * in the bitmap. + * b) All ptes dirtied after that will either remain dirty, be recorded in the + * bitmap or both. + * + * If a caller needs to make sure all dirty ptes are picked up and none + * additional are added, it first needs to write-protect the address-space + * range and make sure new writers are blocked in page_mkwrite() or + * pfn_mkwrite(). And then after a TLB flush following the write-protection + * pick up all dirty bits. + * + * Note: This function currently skips transhuge page-table entries, since + * it's intended for dirty-tracking on the PTE level. It will warn on + * encountering transhuge dirty entries, though, and can easily be extended + * to handle them as well. + * + * Return: The number of dirty ptes actually cleaned. + */ +unsigned long clean_record_shared_mapping_range(struct address_space *mapping, + pgoff_t first_index, pgoff_t nr, + pgoff_t bitmap_pgoff, + unsigned long *bitmap, + pgoff_t *start, + pgoff_t *end) +{ + bool none_set = (*start >= *end); + struct clean_walk cwalk = { + .base = { .total = 0 }, + .bitmap_pgoff = bitmap_pgoff, + .bitmap = bitmap, + .start = none_set ? nr : *start, + .end = none_set ? 0 : *end, + }; + + i_mmap_lock_read(mapping); + WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops, + &cwalk.base)); + i_mmap_unlock_read(mapping); + + *start = cwalk.start; + *end = cwalk.end; + + return cwalk.base.total; +} +EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range); |