Quelle pgtable-generic.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
*  mm/pgtable-generic.c
*
*  Generic pgtable methods declared in linux/pgtable.h
*
*  Copyright (C) 2010  Linus Torvalds
*/

#include <linux/pagemap.h>
#include <linux/hugetlb.h>
#include <linux/pgtable.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mm_inline.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>

/*
* If a p?d_bad entry is found while walking page tables, report
* the error, before resetting entry to p?d_none.  Usually (but
* very seldom) called out from the p?d_none_or_clear_bad macros.
*/

void pgd_clear_bad(pgd_t *pgd)
{
pgd_ERROR(*pgd);
pgd_clear(pgd);
}

#ifndef __PAGETABLE_P4D_FOLDED
void p4d_clear_bad(p4d_t *p4d)
{
p4d_ERROR(*p4d);
p4d_clear(p4d);
}
#endif

#ifndef __PAGETABLE_PUD_FOLDED
void pud_clear_bad(pud_t *pud)
{
pud_ERROR(*pud);
pud_clear(pud);
}
#endif

/*
* Note that the pmd variant below can't be stub'ed out just as for p4d/pud
* above. pmd folding is special and typically pmd_* macros refer to upper
* level even when folded
*/
void pmd_clear_bad(pmd_t *pmd)
{
pmd_ERROR(*pmd);
pmd_clear(pmd);
}

#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
/*
* Only sets the access flags (dirty, accessed), as well as write
* permission. Furthermore, we know it always gets set to a "more
* permissive" setting, which allows most architectures to optimize
* this. We return whether the PTE actually changed, which in turn
* instructs the caller to do things like update__mmu_cache.  This
* used to be done in the caller, but sparc needs minor faults to
* force that call on sun4c so we changed this macro slightly
*/
int ptep_set_access_flags(struct vm_area_struct *vma,
     unsigned long address, pte_t *ptep,
     pte_t entry, int dirty)
{
int changed = !pte_same(ptep_get(ptep), entry);
if (changed) {
  set_pte_at(vma->vm_mm, address, ptep, entry);
  flush_tlb_fix_spurious_fault(vma, address, ptep);
}
return changed;
}
#endif

#ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
int ptep_clear_flush_young(struct vm_area_struct *vma,
      unsigned long address, pte_t *ptep)
{
int young;
young = ptep_test_and_clear_young(vma, address, ptep);
if (young)
  flush_tlb_page(vma, address);
return young;
}
#endif

#ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
         pte_t *ptep)
{
struct mm_struct *mm = (vma)->vm_mm;
pte_t pte;
pte = ptep_get_and_clear(mm, address, ptep);
if (pte_accessible(mm, pte))
  flush_tlb_page(vma, address);
return pte;
}
#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
int pmdp_set_access_flags(struct vm_area_struct *vma,
     unsigned long address, pmd_t *pmdp,
     pmd_t entry, int dirty)
{
int changed = !pmd_same(*pmdp, entry);
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
if (changed) {
  set_pmd_at(vma->vm_mm, address, pmdp, entry);
  flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
}
return changed;
}
#endif

#ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
int pmdp_clear_flush_young(struct vm_area_struct *vma,
      unsigned long address, pmd_t *pmdp)
{
int young;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
young = pmdp_test_and_clear_young(vma, address, pmdp);
if (young)
  flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
return young;
}
#endif

#ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
       pmd_t *pmdp)
{
pmd_t pmd;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp));
pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
return pmd;
}

#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
pud_t pudp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
       pud_t *pudp)
{
pud_t pud;

VM_BUG_ON(address & ~HPAGE_PUD_MASK);
VM_BUG_ON(!pud_trans_huge(*pudp));
pud = pudp_huge_get_and_clear(vma->vm_mm, address, pudp);
flush_pud_tlb_range(vma, address, address + HPAGE_PUD_SIZE);
return pud;
}
#endif
#endif

#ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
    pgtable_t pgtable)
{
assert_spin_locked(pmd_lockptr(mm, pmdp));

/* FIFO */
if (!pmd_huge_pte(mm, pmdp))
  INIT_LIST_HEAD(&pgtable->lru);
else
  list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru);
pmd_huge_pte(mm, pmdp) = pgtable;
}
#endif

#ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
/* no "address" argument so destroys page coloring of some arch */
pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
{
pgtable_t pgtable;

assert_spin_locked(pmd_lockptr(mm, pmdp));

/* FIFO */
pgtable = pmd_huge_pte(mm, pmdp);
pmd_huge_pte(mm, pmdp) = list_first_entry_or_null(&pgtable->lru,
         struct page, lru);
if (pmd_huge_pte(mm, pmdp))
  list_del(&pgtable->lru);
return pgtable;
}
#endif

#ifndef __HAVE_ARCH_PMDP_INVALIDATE
pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
       pmd_t *pmdp)
{
VM_WARN_ON_ONCE(!pmd_present(*pmdp));
pmd_t old = pmdp_establish(vma, address, pmdp, pmd_mkinvalid(*pmdp));
flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
return old;
}
#endif

#ifndef __HAVE_ARCH_PMDP_INVALIDATE_AD
pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address,
    pmd_t *pmdp)
{
VM_WARN_ON_ONCE(!pmd_present(*pmdp));
return pmdp_invalidate(vma, address, pmdp);
}
#endif

#ifndef pmdp_collapse_flush
pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
     pmd_t *pmdp)
{
/*
* pmd and hugepage pte format are same. So we could
* use the same function.
*/
pmd_t pmd;

VM_BUG_ON(address & ~HPAGE_PMD_MASK);
VM_BUG_ON(pmd_trans_huge(*pmdp));
pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);

/* collapse entails shooting down ptes not pmd */
flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
return pmd;
}
#endif

/* arch define pte_free_defer in asm/pgalloc.h for its own implementation */
#ifndef pte_free_defer
static void pte_free_now(struct rcu_head *head)
{
struct page *page;

page = container_of(head, struct page, rcu_head);
pte_free(NULL /* mm not passed and not used */, (pgtable_t)page);
}

void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
{
struct page *page;

page = pgtable;
call_rcu(&page->rcu_head, pte_free_now);
}
#endif /* pte_free_defer */
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \
(defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RCU))
/*
* See the comment above ptep_get_lockless() in include/linux/pgtable.h:
* the barriers in pmdp_get_lockless() cannot guarantee that the value in
* pmd_high actually belongs with the value in pmd_low; but holding interrupts
* off blocks the TLB flush between present updates, which guarantees that a
* successful __pte_offset_map() points to a page from matched halves.
*/
static unsigned long pmdp_get_lockless_start(void)
{
unsigned long irqflags;

local_irq_save(irqflags);
return irqflags;
}
static void pmdp_get_lockless_end(unsigned long irqflags)
{
local_irq_restore(irqflags);
}
#else
static unsigned long pmdp_get_lockless_start(void) { return 0; }
static void pmdp_get_lockless_end(unsigned long irqflags) { }
#endif

pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
{
unsigned long irqflags;
pmd_t pmdval;

rcu_read_lock();
irqflags = pmdp_get_lockless_start();
pmdval = pmdp_get_lockless(pmd);
pmdp_get_lockless_end(irqflags);

if (pmdvalp)
  *pmdvalp = pmdval;
if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))
  goto nomap;
if (unlikely(pmd_trans_huge(pmdval)))
  goto nomap;
if (unlikely(pmd_bad(pmdval))) {
  pmd_clear_bad(pmd);
  goto nomap;
}
return __pte_map(&pmdval, addr);
nomap:
rcu_read_unlock();
return NULL;
}

pte_t *pte_offset_map_ro_nolock(struct mm_struct *mm, pmd_t *pmd,
    unsigned long addr, spinlock_t **ptlp)
{
pmd_t pmdval;
pte_t *pte;

pte = __pte_offset_map(pmd, addr, &pmdval);
if (likely(pte))
  *ptlp = pte_lockptr(mm, &pmdval);
return pte;
}

pte_t *pte_offset_map_rw_nolock(struct mm_struct *mm, pmd_t *pmd,
    unsigned long addr, pmd_t *pmdvalp,
    spinlock_t **ptlp)
{
pte_t *pte;

VM_WARN_ON_ONCE(!pmdvalp);
pte = __pte_offset_map(pmd, addr, pmdvalp);
if (likely(pte))
  *ptlp = pte_lockptr(mm, pmdvalp);
return pte;
}

/*
* pte_offset_map_lock(mm, pmd, addr, ptlp), and its internal implementation
* __pte_offset_map_lock() below, is usually called with the pmd pointer for
* addr, reached by walking down the mm's pgd, p4d, pud for addr: either while
* holding mmap_lock or vma lock for read or for write; or in truncate or rmap
* context, while holding file's i_mmap_lock or anon_vma lock for read (or for
* write). In a few cases, it may be used with pmd pointing to a pmd_t already
* copied to or constructed on the stack.
*
* When successful, it returns the pte pointer for addr, with its page table
* kmapped if necessary (when CONFIG_HIGHPTE), and locked against concurrent
* modification by software, with a pointer to that spinlock in ptlp (in some
* configs mm->page_table_lock, in SPLIT_PTLOCK configs a spinlock in table's
* struct page).  pte_unmap_unlock(pte, ptl) to unlock and unmap afterwards.
*
* But it is unsuccessful, returning NULL with *ptlp unchanged, if there is no
* page table at *pmd: if, for example, the page table has just been removed,
* or replaced by the huge pmd of a THP.  (When successful, *pmd is rechecked
* after acquiring the ptlock, and retried internally if it changed: so that a
* page table can be safely removed or replaced by THP while holding its lock.)
*
* pte_offset_map(pmd, addr), and its internal helper __pte_offset_map() above,
* just returns the pte pointer for addr, its page table kmapped if necessary;
* or NULL if there is no page table at *pmd.  It does not attempt to lock the
* page table, so cannot normally be used when the page table is to be updated,
* or when entries read must be stable.  But it does take rcu_read_lock(): so
* that even when page table is racily removed, it remains a valid though empty
* and disconnected table.  Until pte_unmap(pte) unmaps and rcu_read_unlock()s
* afterwards.
*
* pte_offset_map_ro_nolock(mm, pmd, addr, ptlp), above, is like pte_offset_map();
* but when successful, it also outputs a pointer to the spinlock in ptlp - as
* pte_offset_map_lock() does, but in this case without locking it.  This helps
* the caller to avoid a later pte_lockptr(mm, *pmd), which might by that time
* act on a changed *pmd: pte_offset_map_ro_nolock() provides the correct spinlock
* pointer for the page table that it returns. Even after grabbing the spinlock,
* we might be looking either at a page table that is still mapped or one that
* was unmapped and is about to get freed. But for R/O access this is sufficient.
* So it is only applicable for read-only cases where any modification operations
* to the page table are not allowed even if the corresponding spinlock is held
* afterwards.
*
* pte_offset_map_rw_nolock(mm, pmd, addr, pmdvalp, ptlp), above, is like
* pte_offset_map_ro_nolock(); but when successful, it also outputs the pdmval.
* It is applicable for may-write cases where any modification operations to the
* page table may happen after the corresponding spinlock is held afterwards.
* But the users should make sure the page table is stable like checking pte_same()
* or checking pmd_same() by using the output pmdval before performing the write
* operations.
*
* Note: "RO" / "RW" expresses the intended semantics, not that the *kmap* will
* be read-only/read-write protected.
*
* Note that free_pgtables(), used after unmapping detached vmas, or when
* exiting the whole mm, does not take page table lock before freeing a page
* table, and may not use RCU at all: "outsiders" like khugepaged should avoid
* pte_offset_map() and co once the vma is detached from mm or mm_users is zero.
*/
pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd,
        unsigned long addr, spinlock_t **ptlp)
{
spinlock_t *ptl;
pmd_t pmdval;
pte_t *pte;
again:
pte = __pte_offset_map(pmd, addr, &pmdval);
if (unlikely(!pte))
  return pte;
ptl = pte_lockptr(mm, &pmdval);
spin_lock(ptl);
if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
  *ptlp = ptl;
  return pte;
}
pte_unmap_unlock(pte, ptl);
goto again;
}

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