// SPDX-License-Identifier: GPL-2.0
#include <linux/pagewalk.h>
#include <linux/hugetlb.h>
#include <linux/bitops.h>
#include <linux/mmu_notifier.h>
#include <linux/mm_inline.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 start of protecting virtual address
* @end: The end of protecting virtual 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 start of virtual address to be clean
* @end: The end of virtual address to be clean
* @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 = pmdp_get_lockless(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;
}
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
/* Huge pud */
walk->action = ACTION_CONTINUE;
if (pud_trans_huge(pudval) || pud_devmap(pudval))
WARN_ON(pud_write(pudval) || pud_dirty(pudval));
#endif
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->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.
*
* 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);
