if (!new)
return -ENOMEM;
+ /*
+ * Ensure all pte setup (eg. pte page lock and page clearing) are
+ * visible before the pte is made visible to other CPUs by being
+ * put into page tables.
+ *
+ * The other side of the story is the pointer chasing in the page
+ * table walking code (when walking the page table without locking;
+ * ie. most of the time). Fortunately, these data accesses consist
+ * of a chain of data-dependent loads, meaning most CPUs (alpha
+ * being the notable exception) will already guarantee loads are
+ * seen in-order. See the alpha page table accessors for the
+ * smp_read_barrier_depends() barriers in page table walking code.
+ */
+ smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
+
spin_lock(&mm->page_table_lock);
if (!pmd_present(*pmd)) { /* Has another populated it ? */
mm->nr_ptes++;
if (!new)
return -ENOMEM;
+ smp_wmb(); /* See comment in __pte_alloc */
+
spin_lock(&init_mm.page_table_lock);
if (!pmd_present(*pmd)) { /* Has another populated it ? */
pmd_populate_kernel(&init_mm, pmd, new);
}
/*
- * This function gets the "struct page" associated with a pte.
+ * vm_normal_page -- This function gets the "struct page" associated with a pte.
+ *
+ * "Special" mappings do not wish to be associated with a "struct page" (either
+ * it doesn't exist, or it exists but they don't want to touch it). In this
+ * case, NULL is returned here. "Normal" mappings do have a struct page.
*
- * NOTE! Some mappings do not have "struct pages". A raw PFN mapping
- * will have each page table entry just pointing to a raw page frame
- * number, and as far as the VM layer is concerned, those do not have
- * pages associated with them - even if the PFN might point to memory
- * that otherwise is perfectly fine and has a "struct page".
+ * There are 2 broad cases. Firstly, an architecture may define a pte_special()
+ * pte bit, in which case this function is trivial. Secondly, an architecture
+ * may not have a spare pte bit, which requires a more complicated scheme,
+ * described below.
*
- * The way we recognize those mappings is through the rules set up
- * by "remap_pfn_range()": the vma will have the VM_PFNMAP bit set,
- * and the vm_pgoff will point to the first PFN mapped: thus every
- * page that is a raw mapping will always honor the rule
+ * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
+ * special mapping (even if there are underlying and valid "struct pages").
+ * COWed pages of a VM_PFNMAP are always normal.
+ *
+ * The way we recognize COWed pages within VM_PFNMAP mappings is through the
+ * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
+ * set, and the vm_pgoff will point to the first PFN mapped: thus every special
+ * mapping will always honor the rule
*
* pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
*
- * and if that isn't true, the page has been COW'ed (in which case it
- * _does_ have a "struct page" associated with it even if it is in a
- * VM_PFNMAP range).
+ * And for normal mappings this is false.
+ *
+ * This restricts such mappings to be a linear translation from virtual address
+ * to pfn. To get around this restriction, we allow arbitrary mappings so long
+ * as the vma is not a COW mapping; in that case, we know that all ptes are
+ * special (because none can have been COWed).
+ *
+ *
+ * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
+ *
+ * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
+ * page" backing, however the difference is that _all_ pages with a struct
+ * page (that is, those where pfn_valid is true) are refcounted and considered
+ * normal pages by the VM. The disadvantage is that pages are refcounted
+ * (which can be slower and simply not an option for some PFNMAP users). The
+ * advantage is that we don't have to follow the strict linearity rule of
+ * PFNMAP mappings in order to support COWable mappings.
+ *
*/
-struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
+#ifdef __HAVE_ARCH_PTE_SPECIAL
+# define HAVE_PTE_SPECIAL 1
+#else
+# define HAVE_PTE_SPECIAL 0
+#endif
+struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
+ pte_t pte)
{
- unsigned long pfn = pte_pfn(pte);
+ unsigned long pfn;
- if (unlikely(vma->vm_flags & VM_PFNMAP)) {
- unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
- if (pfn == vma->vm_pgoff + off)
- return NULL;
- if (!is_cow_mapping(vma->vm_flags))
- return NULL;
+ if (HAVE_PTE_SPECIAL) {
+ if (likely(!pte_special(pte))) {
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+ return pte_page(pte);
+ }
+ VM_BUG_ON(!(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
+ return NULL;
}
-#ifdef CONFIG_DEBUG_VM
- /*
- * Add some anal sanity checks for now. Eventually,
- * we should just do "return pfn_to_page(pfn)", but
- * in the meantime we check that we get a valid pfn,
- * and that the resulting page looks ok.
- */
- if (unlikely(!pfn_valid(pfn))) {
- print_bad_pte(vma, pte, addr);
- return NULL;
+ /* !HAVE_PTE_SPECIAL case follows: */
+
+ pfn = pte_pfn(pte);
+
+ if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
+ if (vma->vm_flags & VM_MIXEDMAP) {
+ if (!pfn_valid(pfn))
+ return NULL;
+ goto out;
+ } else {
+ unsigned long off;
+ off = (addr - vma->vm_start) >> PAGE_SHIFT;
+ if (pfn == vma->vm_pgoff + off)
+ return NULL;
+ if (!is_cow_mapping(vma->vm_flags))
+ return NULL;
+ }
}
-#endif
+
+ VM_BUG_ON(!pfn_valid(pfn));
/*
- * NOTE! We still have PageReserved() pages in the page
- * tables.
+ * NOTE! We still have PageReserved() pages in the page tables.
*
- * The PAGE_ZERO() pages and various VDSO mappings can
- * cause them to exist.
+ * eg. VDSO mappings can cause them to exist.
*/
+out:
return pfn_to_page(pfn);
}
goto no_page_table;
pmd = pmd_offset(pud, address);
- if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+ if (pmd_none(*pmd))
goto no_page_table;
if (pmd_huge(*pmd)) {
goto out;
}
+ if (unlikely(pmd_bad(*pmd)))
+ goto no_page_table;
+
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
- if (!ptep)
- goto out;
pte = *ptep;
if (!pte_present(pte))
- goto unlock;
+ goto no_page;
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
page = vm_normal_page(vma, address, pte);
if (unlikely(!page))
- goto unlock;
+ goto bad_page;
if (flags & FOLL_GET)
get_page(page);
out:
return page;
+bad_page:
+ pte_unmap_unlock(ptep, ptl);
+ return ERR_PTR(-EFAULT);
+
+no_page:
+ pte_unmap_unlock(ptep, ptl);
+ if (!pte_none(pte))
+ return page;
+ /* Fall through to ZERO_PAGE handling */
no_page_table:
/*
* When core dumping an enormous anonymous area that nobody
return page;
}
+/* Can we do the FOLL_ANON optimization? */
+static inline int use_zero_page(struct vm_area_struct *vma)
+{
+ /*
+ * We don't want to optimize FOLL_ANON for make_pages_present()
+ * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
+ * we want to get the page from the page tables to make sure
+ * that we serialize and update with any other user of that
+ * mapping.
+ */
+ if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
+ return 0;
+ /*
+ * And if we have a fault or a nopfn routine, it's not an
+ * anonymous region.
+ */
+ return !vma->vm_ops ||
+ (!vma->vm_ops->fault && !vma->vm_ops->nopfn);
+}
+
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, int write, int force,
struct page **pages, struct vm_area_struct **vmas)
foll_flags = FOLL_TOUCH;
if (pages)
foll_flags |= FOLL_GET;
- if (!write && !(vma->vm_flags & VM_LOCKED) &&
- (!vma->vm_ops || (!vma->vm_ops->nopage &&
- !vma->vm_ops->fault)))
+ if (!write && use_zero_page(vma))
foll_flags |= FOLL_ANON;
do {
* be processed until returning to user space.
*/
if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
- return -ENOMEM;
+ return i ? i : -ENOMEM;
if (write)
foll_flags |= FOLL_WRITE;
cond_resched();
}
+ if (IS_ERR(page))
+ return i ? i : PTR_ERR(page);
if (pages) {
pages[i] = page;
* old drivers should use this, and they needed to mark their
* pages reserved for the old functions anyway.
*/
-static int insert_page(struct mm_struct *mm, unsigned long addr, struct page *page, pgprot_t prot)
+static int insert_page(struct vm_area_struct *vma, unsigned long addr,
+ struct page *page, pgprot_t prot)
{
+ struct mm_struct *mm = vma->vm_mm;
int retval;
pte_t *pte;
spinlock_t *ptl;
*
* The page does not need to be reserved.
*/
-int vm_insert_page(struct vm_area_struct *vma, unsigned long addr, struct page *page)
+int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
+ struct page *page)
{
if (addr < vma->vm_start || addr >= vma->vm_end)
return -EFAULT;
if (!page_count(page))
return -EINVAL;
vma->vm_flags |= VM_INSERTPAGE;
- return insert_page(vma->vm_mm, addr, page, vma->vm_page_prot);
+ return insert_page(vma, addr, page, vma->vm_page_prot);
}
EXPORT_SYMBOL(vm_insert_page);
-/**
- * vm_insert_pfn - insert single pfn into user vma
- * @vma: user vma to map to
- * @addr: target user address of this page
- * @pfn: source kernel pfn
- *
- * Similar to vm_inert_page, this allows drivers to insert individual pages
- * they've allocated into a user vma. Same comments apply.
- *
- * This function should only be called from a vm_ops->fault handler, and
- * in that case the handler should return NULL.
- */
-int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
- unsigned long pfn)
+static int insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+ unsigned long pfn, pgprot_t prot)
{
struct mm_struct *mm = vma->vm_mm;
int retval;
pte_t *pte, entry;
spinlock_t *ptl;
- BUG_ON(!(vma->vm_flags & VM_PFNMAP));
- BUG_ON(is_cow_mapping(vma->vm_flags));
-
retval = -ENOMEM;
pte = get_locked_pte(mm, addr, &ptl);
if (!pte)
goto out_unlock;
/* Ok, finally just insert the thing.. */
- entry = pfn_pte(pfn, vma->vm_page_prot);
+ entry = pte_mkspecial(pfn_pte(pfn, prot));
set_pte_at(mm, addr, pte, entry);
- update_mmu_cache(vma, addr, entry);
+ update_mmu_cache(vma, addr, entry); /* XXX: why not for insert_page? */
retval = 0;
out_unlock:
pte_unmap_unlock(pte, ptl);
-
out:
return retval;
}
+
+/**
+ * vm_insert_pfn - insert single pfn into user vma
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ *
+ * Similar to vm_inert_page, this allows drivers to insert individual pages
+ * they've allocated into a user vma. Same comments apply.
+ *
+ * This function should only be called from a vm_ops->fault handler, and
+ * in that case the handler should return NULL.
+ */
+int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+ unsigned long pfn)
+{
+ /*
+ * Technically, architectures with pte_special can avoid all these
+ * restrictions (same for remap_pfn_range). However we would like
+ * consistency in testing and feature parity among all, so we should
+ * try to keep these invariants in place for everybody.
+ */
+ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+ BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
+ (VM_PFNMAP|VM_MIXEDMAP));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+ BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return -EFAULT;
+ return insert_pfn(vma, addr, pfn, vma->vm_page_prot);
+}
EXPORT_SYMBOL(vm_insert_pfn);
+int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
+ unsigned long pfn)
+{
+ BUG_ON(!(vma->vm_flags & VM_MIXEDMAP));
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return -EFAULT;
+
+ /*
+ * If we don't have pte special, then we have to use the pfn_valid()
+ * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
+ * refcount the page if pfn_valid is true (hence insert_page rather
+ * than insert_pfn).
+ */
+ if (!HAVE_PTE_SPECIAL && pfn_valid(pfn)) {
+ struct page *page;
+
+ page = pfn_to_page(pfn);
+ return insert_page(vma, addr, page, vma->vm_page_prot);
+ }
+ return insert_pfn(vma, addr, pfn, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_mixed);
+
/*
* maps a range of physical memory into the requested pages. the old
* mappings are removed. any references to nonexistent pages results
arch_enter_lazy_mmu_mode();
do {
BUG_ON(!pte_none(*pte));
- set_pte_at(mm, addr, pte, pfn_pte(pfn, prot));
+ set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
pfn++;
} while (pte++, addr += PAGE_SIZE, addr != end);
arch_leave_lazy_mmu_mode();
struct page *dirty_page = NULL;
old_page = vm_normal_page(vma, address, orig_pte);
- if (!old_page)
+ if (!old_page) {
+ /*
+ * VM_MIXEDMAP !pfn_valid() case
+ *
+ * We should not cow pages in a shared writeable mapping.
+ * Just mark the pages writable as we can't do any dirty
+ * accounting on raw pfn maps.
+ */
+ if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
+ (VM_WRITE|VM_SHARED))
+ goto reuse;
goto gotten;
+ }
/*
* Take out anonymous pages first, anonymous shared vmas are
}
if (reuse) {
+reuse:
flush_cache_page(vma, address, pte_pfn(orig_pte));
entry = pte_mkyoung(orig_pte);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (likely(pte_same(*page_table, orig_pte))) {
if (old_page) {
- page_remove_rmap(old_page, vma);
if (!PageAnon(old_page)) {
dec_mm_counter(mm, file_rss);
inc_mm_counter(mm, anon_rss);
lru_cache_add_active(new_page);
page_add_new_anon_rmap(new_page, vma, address);
+ if (old_page) {
+ /*
+ * Only after switching the pte to the new page may
+ * we remove the mapcount here. Otherwise another
+ * process may come and find the rmap count decremented
+ * before the pte is switched to the new page, and
+ * "reuse" the old page writing into it while our pte
+ * here still points into it and can be read by other
+ * threads.
+ *
+ * The critical issue is to order this
+ * page_remove_rmap with the ptp_clear_flush above.
+ * Those stores are ordered by (if nothing else,)
+ * the barrier present in the atomic_add_negative
+ * in page_remove_rmap.
+ *
+ * Then the TLB flush in ptep_clear_flush ensures that
+ * no process can access the old page before the
+ * decremented mapcount is visible. And the old page
+ * cannot be reused until after the decremented
+ * mapcount is visible. So transitively, TLBs to
+ * old page will be flushed before it can be reused.
+ */
+ page_remove_rmap(old_page, vma);
+ }
+
/* Free the old page.. */
new_page = old_page;
ret |= VM_FAULT_WRITE;
vmf.flags = flags;
vmf.page = NULL;
- BUG_ON(vma->vm_flags & VM_PFNMAP);
-
- if (likely(vma->vm_ops->fault)) {
- ret = vma->vm_ops->fault(vma, &vmf);
- if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
- return ret;
- } else {
- /* Legacy ->nopage path */
- ret = 0;
- vmf.page = vma->vm_ops->nopage(vma, address & PAGE_MASK, &ret);
- /* no page was available -- either SIGBUS or OOM */
- if (unlikely(vmf.page == NOPAGE_SIGBUS))
- return VM_FAULT_SIGBUS;
- else if (unlikely(vmf.page == NOPAGE_OOM))
- return VM_FAULT_OOM;
- }
+ ret = vma->vm_ops->fault(vma, &vmf);
+ if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
+ return ret;
/*
* For consistency in subsequent calls, make the faulted page always
unsigned long pfn;
pte_unmap(page_table);
- BUG_ON(!(vma->vm_flags & VM_PFNMAP));
- BUG_ON(is_cow_mapping(vma->vm_flags));
+ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
pfn = vma->vm_ops->nopfn(vma, address & PAGE_MASK);
+
+ BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
+
if (unlikely(pfn == NOPFN_OOM))
return VM_FAULT_OOM;
else if (unlikely(pfn == NOPFN_SIGBUS))
if (!pte_present(entry)) {
if (pte_none(entry)) {
if (vma->vm_ops) {
- if (vma->vm_ops->fault || vma->vm_ops->nopage)
+ if (likely(vma->vm_ops->fault))
return do_linear_fault(mm, vma, address,
pte, pmd, write_access, entry);
if (unlikely(vma->vm_ops->nopfn))
if (!new)
return -ENOMEM;
+ smp_wmb(); /* See comment in __pte_alloc */
+
spin_lock(&mm->page_table_lock);
if (pgd_present(*pgd)) /* Another has populated it */
pud_free(mm, new);
if (!new)
return -ENOMEM;
+ smp_wmb(); /* See comment in __pte_alloc */
+
spin_lock(&mm->page_table_lock);
#ifndef __ARCH_HAS_4LEVEL_HACK
if (pud_present(*pud)) /* Another has populated it */
projects / linux-2.6 / blobdiff