2 files changed, 188 insertions, 126 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 54d5318..1efd299 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2144,11 +2144,6 @@ void filemap_map_pages(struct fault_env *fe,
 			start_pgoff) {
 		if (iter.index > end_pgoff)
 			break;
-		fe->pte += iter.index - last_pgoff;
-		fe->address += (iter.index - last_pgoff) << PAGE_SHIFT;
-		last_pgoff = iter.index;
-		if (!pte_none(*fe->pte))
-			goto next;
 repeat:
 		page = radix_tree_deref_slot(slot);
 		if (unlikely(!page))
@@ -2186,7 +2181,13 @@ repeat:
 
 		if (file->f_ra.mmap_miss > 0)
 			file->f_ra.mmap_miss--;
-		do_set_pte(fe, page);
+
+		fe->address += (iter.index - last_pgoff) << PAGE_SHIFT;
+		if (fe->pte)
+			fe->pte += iter.index - last_pgoff;
+		last_pgoff = iter.index;
+		if (alloc_set_pte(fe, NULL, page))
+			goto unlock;
 		unlock_page(page);
 		goto next;
 unlock:
@@ -2194,6 +2195,9 @@ unlock:
 skip:
 		put_page(page);
 next:
+		/* Huge page is mapped? No need to proceed. */
+		if (pmd_trans_huge(*fe->pmd))
+			break;
 		if (iter.index == end_pgoff)
 			break;
 	}
diff --git a/mm/memory.c b/mm/memory.c
index 72b5208..1991105 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2739,8 +2739,6 @@ static int do_anonymous_page(struct fault_env *fe)
 	struct page *page;
 	pte_t entry;
 
-	pte_unmap(fe->pte);
-
 	/* File mapping without ->vm_ops ? */
 	if (vma->vm_flags & VM_SHARED)
 		return VM_FAULT_SIGBUS;
@@ -2749,6 +2747,23 @@ static int do_anonymous_page(struct fault_env *fe)
 	if (check_stack_guard_page(vma, fe->address) < 0)
 		return VM_FAULT_SIGSEGV;
 
+	/*
+	 * Use pte_alloc() instead of pte_alloc_map().  We can't run
+	 * pte_offset_map() on pmds where a huge pmd might be created
+	 * from a different thread.
+	 *
+	 * pte_alloc_map() is safe to use under down_write(mmap_sem) or when
+	 * parallel threads are excluded by other means.
+	 *
+	 * Here we only have down_read(mmap_sem).
+	 */
+	if (pte_alloc(vma->vm_mm, fe->pmd, fe->address))
+		return VM_FAULT_OOM;
+
+	/* See the comment in pte_alloc_one_map() */
+	if (unlikely(pmd_trans_unstable(fe->pmd)))
+		return 0;
+
 	/* Use the zero-page for reads */
 	if (!(fe->flags & FAULT_FLAG_WRITE) &&
 			!mm_forbids_zeropage(vma->vm_mm)) {
@@ -2865,23 +2880,76 @@ static int __do_fault(struct fault_env *fe, pgoff_t pgoff,
 	return ret;
 }
 
+static int pte_alloc_one_map(struct fault_env *fe)
+{
+	struct vm_area_struct *vma = fe->vma;
+
+	if (!pmd_none(*fe->pmd))
+		goto map_pte;
+	if (fe->prealloc_pte) {
+		fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
+		if (unlikely(!pmd_none(*fe->pmd))) {
+			spin_unlock(fe->ptl);
+			goto map_pte;
+		}
+
+		atomic_long_inc(&vma->vm_mm->nr_ptes);
+		pmd_populate(vma->vm_mm, fe->pmd, fe->prealloc_pte);
+		spin_unlock(fe->ptl);
+		fe->prealloc_pte = 0;
+	} else if (unlikely(pte_alloc(vma->vm_mm, fe->pmd, fe->address))) {
+		return VM_FAULT_OOM;
+	}
+map_pte:
+	/*
+	 * If a huge pmd materialized under us just retry later.  Use
+	 * pmd_trans_unstable() instead of pmd_trans_huge() to ensure the pmd
+	 * didn't become pmd_trans_huge under us and then back to pmd_none, as
+	 * a result of MADV_DONTNEED running immediately after a huge pmd fault
+	 * in a different thread of this mm, in turn leading to a misleading
+	 * pmd_trans_huge() retval.  All we have to ensure is that it is a
+	 * regular pmd that we can walk with pte_offset_map() and we can do that
+	 * through an atomic read in C, which is what pmd_trans_unstable()
+	 * provides.
+	 */
+	if (pmd_trans_unstable(fe->pmd) || pmd_devmap(*fe->pmd))
+		return VM_FAULT_NOPAGE;
+
+	fe->pte = pte_offset_map_lock(vma->vm_mm, fe->pmd, fe->address,
+			&fe->ptl);
+	return 0;
+}
+
 /**
- * do_set_pte - setup new PTE entry for given page and add reverse page mapping.
+ * alloc_set_pte - setup new PTE entry for given page and add reverse page
+ * mapping. If needed, the fucntion allocates page table or use pre-allocated.
  *
  * @fe: fault environment
+ * @memcg: memcg to charge page (only for private mappings)
  * @page: page to map
  *
- * Caller must hold page table lock relevant for @fe->pte.
+ * Caller must take care of unlocking fe->ptl, if fe->pte is non-NULL on return.
  *
  * Target users are page handler itself and implementations of
  * vm_ops->map_pages.
  */
-void do_set_pte(struct fault_env *fe, struct page *page)
+int alloc_set_pte(struct fault_env *fe, struct mem_cgroup *memcg,
+		struct page *page)
 {
 	struct vm_area_struct *vma = fe->vma;
 	bool write = fe->flags & FAULT_FLAG_WRITE;
 	pte_t entry;
 
+	if (!fe->pte) {
+		int ret = pte_alloc_one_map(fe);
+		if (ret)
+			return ret;
+	}
+
+	/* Re-check under ptl */
+	if (unlikely(!pte_none(*fe->pte)))
+		return VM_FAULT_NOPAGE;
+
 	flush_icache_page(vma, page);
 	entry = mk_pte(page, vma->vm_page_prot);
 	if (write)
@@ -2890,6 +2958,8 @@ void do_set_pte(struct fault_env *fe, struct page *page)
 	if (write && !(vma->vm_flags & VM_SHARED)) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 		page_add_new_anon_rmap(page, vma, fe->address, false);
+		mem_cgroup_commit_charge(page, memcg, false, false);
+		lru_cache_add_active_or_unevictable(page, vma);
 	} else {
 		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
 		page_add_file_rmap(page);
@@ -2898,6 +2968,8 @@ void do_set_pte(struct fault_env *fe, struct page *page)
 
 	/* no need to invalidate: a not-present page won't be cached */
 	update_mmu_cache(vma, fe->address, fe->pte);
+
+	return 0;
 }
 
 static unsigned long fault_around_bytes __read_mostly =
@@ -2964,19 +3036,17 @@ late_initcall(fault_around_debugfs);
  * fault_around_pages() value (and therefore to page order).  This way it's
  * easier to guarantee that we don't cross page table boundaries.
  */
-static void do_fault_around(struct fault_env *fe, pgoff_t start_pgoff)
+static int do_fault_around(struct fault_env *fe, pgoff_t start_pgoff)
 {
-	unsigned long address = fe->address, start_addr, nr_pages, mask;
-	pte_t *pte = fe->pte;
+	unsigned long address = fe->address, nr_pages, mask;
 	pgoff_t end_pgoff;
-	int off;
+	int off, ret = 0;
 
 	nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT;
 	mask = ~(nr_pages * PAGE_SIZE - 1) & PAGE_MASK;
 
-	start_addr = max(fe->address & mask, fe->vma->vm_start);
-	off = ((fe->address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
-	fe->pte -= off;
+	fe->address = max(address & mask, fe->vma->vm_start);
+	off = ((address - fe->address) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
 	start_pgoff -= off;
 
 	/*
@@ -2984,30 +3054,45 @@ static void do_fault_around(struct fault_env *fe, pgoff_t start_pgoff)
 	 *  or fault_around_pages() from start_pgoff, depending what is nearest.
 	 */
 	end_pgoff = start_pgoff -
-		((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
+		((fe->address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
 		PTRS_PER_PTE - 1;
 	end_pgoff = min3(end_pgoff, vma_pages(fe->vma) + fe->vma->vm_pgoff - 1,
 			start_pgoff + nr_pages - 1);
 
-	/* Check if it makes any sense to call ->map_pages */
-	fe->address = start_addr;
-	while (!pte_none(*fe->pte)) {
-		if (++start_pgoff > end_pgoff)
-			goto out;
-		fe->address += PAGE_SIZE;
-		if (fe->address >= fe->vma->vm_end)
-			goto out;
-		fe->pte++;
+	if (pmd_none(*fe->pmd)) {
+		fe->prealloc_pte = pte_alloc_one(fe->vma->vm_mm, fe->address);
+		smp_wmb(); /* See comment in __pte_alloc() */
 	}
 
 	fe->vma->vm_ops->map_pages(fe, start_pgoff, end_pgoff);
+
+	/* preallocated pagetable is unused: free it */
+	if (fe->prealloc_pte) {
+		pte_free(fe->vma->vm_mm, fe->prealloc_pte);
+		fe->prealloc_pte = 0;
+	}
+	/* Huge page is mapped? Page fault is solved */
+	if (pmd_trans_huge(*fe->pmd)) {
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+
+	/* ->map_pages() haven't done anything useful. Cold page cache? */
+	if (!fe->pte)
+		goto out;
+
+	/* check if the page fault is solved */
+	fe->pte -= (fe->address >> PAGE_SHIFT) - (address >> PAGE_SHIFT);
+	if (!pte_none(*fe->pte))
+		ret = VM_FAULT_NOPAGE;
+	pte_unmap_unlock(fe->pte, fe->ptl);
 out:
-	/* restore fault_env */
-	fe->pte = pte;
 	fe->address = address;
+	fe->pte = NULL;
+	return ret;
 }
 
-static int do_read_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
+static int do_read_fault(struct fault_env *fe, pgoff_t pgoff)
 {
 	struct vm_area_struct *vma = fe->vma;
 	struct page *fault_page;
@@ -3019,36 +3104,25 @@ static int do_read_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
 	 * something).
 	 */
 	if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
-		fe->pte = pte_offset_map_lock(vma->vm_mm, fe->pmd, fe->address,
-				&fe->ptl);
-		if (!pte_same(*fe->pte, orig_pte))
-			goto unlock_out;
-		do_fault_around(fe, pgoff);
-		/* Check if the fault is handled by faultaround */
-		if (!pte_same(*fe->pte, orig_pte))
-			goto unlock_out;
-		pte_unmap_unlock(fe->pte, fe->ptl);
+		ret = do_fault_around(fe, pgoff);
+		if (ret)
+			return ret;
 	}
 
 	ret = __do_fault(fe, pgoff, NULL, &fault_page, NULL);
 	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
 		return ret;
 
-	fe->pte = pte_offset_map_lock(vma->vm_mm, fe->pmd, fe->address, &fe->ptl);
-	if (unlikely(!pte_same(*fe->pte, orig_pte))) {
+	ret |= alloc_set_pte(fe, NULL, fault_page);
+	if (fe->pte)
 		pte_unmap_unlock(fe->pte, fe->ptl);
-		unlock_page(fault_page);
-		put_page(fault_page);
-		return ret;
-	}
-	do_set_pte(fe, fault_page);
 	unlock_page(fault_page);
-unlock_out:
-	pte_unmap_unlock(fe->pte, fe->ptl);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		put_page(fault_page);
 	return ret;
 }
 
-static int do_cow_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
+static int do_cow_fault(struct fault_env *fe, pgoff_t pgoff)
 {
 	struct vm_area_struct *vma = fe->vma;
 	struct page *fault_page, *new_page;
@@ -3077,29 +3151,17 @@ static int do_cow_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
 		copy_user_highpage(new_page, fault_page, fe->address, vma);
 	__SetPageUptodate(new_page);
 
-	fe->pte = pte_offset_map_lock(vma->vm_mm, fe->pmd, fe->address,
-			&fe->ptl);
-	if (unlikely(!pte_same(*fe->pte, orig_pte))) {
+	ret |= alloc_set_pte(fe, memcg, new_page);
+	if (fe->pte)
 		pte_unmap_unlock(fe->pte, fe->ptl);
-		if (!(ret & VM_FAULT_DAX_LOCKED)) {
-			unlock_page(fault_page);
-			put_page(fault_page);
-		} else {
-			dax_unlock_mapping_entry(vma->vm_file->f_mapping,
-						 pgoff);
-		}
-		goto uncharge_out;
-	}
-	do_set_pte(fe, new_page);
-	mem_cgroup_commit_charge(new_page, memcg, false, false);
-	lru_cache_add_active_or_unevictable(new_page, vma);
-	pte_unmap_unlock(fe->pte, fe->ptl);
 	if (!(ret & VM_FAULT_DAX_LOCKED)) {
 		unlock_page(fault_page);
 		put_page(fault_page);
 	} else {
 		dax_unlock_mapping_entry(vma->vm_file->f_mapping, pgoff);
 	}
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		goto uncharge_out;
 	return ret;
 uncharge_out:
 	mem_cgroup_cancel_charge(new_page, memcg, false);
@@ -3107,7 +3169,7 @@ uncharge_out:
 	return ret;
 }
 
-static int do_shared_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
+static int do_shared_fault(struct fault_env *fe, pgoff_t pgoff)
 {
 	struct vm_area_struct *vma = fe->vma;
 	struct page *fault_page;
@@ -3133,16 +3195,15 @@ static int do_shared_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
 		}
 	}
 
-	fe->pte = pte_offset_map_lock(vma->vm_mm, fe->pmd, fe->address,
-			&fe->ptl);
-	if (unlikely(!pte_same(*fe->pte, orig_pte))) {
+	ret |= alloc_set_pte(fe, NULL, fault_page);
+	if (fe->pte)
 		pte_unmap_unlock(fe->pte, fe->ptl);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
+					VM_FAULT_RETRY))) {
 		unlock_page(fault_page);
 		put_page(fault_page);
 		return ret;
 	}
-	do_set_pte(fe, fault_page);
-	pte_unmap_unlock(fe->pte, fe->ptl);
 
 	if (set_page_dirty(fault_page))
 		dirtied = 1;
@@ -3174,20 +3235,19 @@ static int do_shared_fault(struct fault_env *fe, pgoff_t pgoff, pte_t orig_pte)
  * The mmap_sem may have been released depending on flags and our
  * return value.  See filemap_fault() and __lock_page_or_retry().
  */
-static int do_fault(struct fault_env *fe, pte_t orig_pte)
+static int do_fault(struct fault_env *fe)
 {
 	struct vm_area_struct *vma = fe->vma;
 	pgoff_t pgoff = linear_page_index(vma, fe->address);
 
-	pte_unmap(fe->pte);
 	/* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
 	if (!vma->vm_ops->fault)
 		return VM_FAULT_SIGBUS;
 	if (!(fe->flags & FAULT_FLAG_WRITE))
-		return do_read_fault(fe, pgoff,	orig_pte);
+		return do_read_fault(fe, pgoff);
 	if (!(vma->vm_flags & VM_SHARED))
-		return do_cow_fault(fe, pgoff, orig_pte);
-	return do_shared_fault(fe, pgoff, orig_pte);
+		return do_cow_fault(fe, pgoff);
+	return do_shared_fault(fe, pgoff);
 }
 
 static int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
@@ -3327,37 +3387,63 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd)
  * with external mmu caches can use to update those (ie the Sparc or
  * PowerPC hashed page tables that act as extended TLBs).
  *
- * We enter with non-exclusive mmap_sem (to exclude vma changes,
- * but allow concurrent faults), and pte mapped but not yet locked.
- * We return with pte unmapped and unlocked.
+ * We enter with non-exclusive mmap_sem (to exclude vma changes, but allow
+ * concurrent faults).
  *
- * The mmap_sem may have been released depending on flags and our
- * return value.  See filemap_fault() and __lock_page_or_retry().
+ * The mmap_sem may have been released depending on flags and our return value.
+ * See filemap_fault() and __lock_page_or_retry().
  */
 static int handle_pte_fault(struct fault_env *fe)
 {
 	pte_t entry;
 
-	/*
-	 * some architectures can have larger ptes than wordsize,
-	 * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and CONFIG_32BIT=y,
-	 * so READ_ONCE or ACCESS_ONCE cannot guarantee atomic accesses.
-	 * The code below just needs a consistent view for the ifs and
-	 * we later double check anyway with the ptl lock held. So here
-	 * a barrier will do.
-	 */
-	entry = *fe->pte;
-	barrier();
-	if (!pte_present(entry)) {
+	if (unlikely(pmd_none(*fe->pmd))) {
+		/*
+		 * Leave __pte_alloc() until later: because vm_ops->fault may
+		 * want to allocate huge page, and if we expose page table
+		 * for an instant, it will be difficult to retract from
+		 * concurrent faults and from rmap lookups.
+		 */
+		fe->pte = NULL;
+	} else {
+		/* See comment in pte_alloc_one_map() */
+		if (pmd_trans_unstable(fe->pmd) || pmd_devmap(*fe->pmd))
+			return 0;
+		/*
+		 * A regular pmd is established and it can't morph into a huge
+		 * pmd from under us anymore at this point because we hold the
+		 * mmap_sem read mode and khugepaged takes it in write mode.
+		 * So now it's safe to run pte_offset_map().
+		 */
+		fe->pte = pte_offset_map(fe->pmd, fe->address);
+
+		entry = *fe->pte;
+
+		/*
+		 * some architectures can have larger ptes than wordsize,
+		 * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and
+		 * CONFIG_32BIT=y, so READ_ONCE or ACCESS_ONCE cannot guarantee
+		 * atomic accesses.  The code below just needs a consistent
+		 * view for the ifs and we later double check anyway with the
+		 * ptl lock held. So here a barrier will do.
+		 */
+		barrier();
 		if (pte_none(entry)) {
-			if (vma_is_anonymous(fe->vma))
-				return do_anonymous_page(fe);
-			else
-				return do_fault(fe, entry);
+			pte_unmap(fe->pte);
+			fe->pte = NULL;
 		}
-		return do_swap_page(fe, entry);
 	}
 
+	if (!fe->pte) {
+		if (vma_is_anonymous(fe->vma))
+			return do_anonymous_page(fe);
+		else
+			return do_fault(fe);
+	}
+
+	if (!pte_present(entry))
+		return do_swap_page(fe, entry);
+
 	if (pte_protnone(entry))
 		return do_numa_page(fe, entry);
 
@@ -3439,34 +3525,6 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 		}
 	}
 
-	/*
-	 * Use pte_alloc() instead of pte_alloc_map, because we can't
-	 * run pte_offset_map on the pmd, if an huge pmd could
-	 * materialize from under us from a different thread.
-	 */
-	if (unlikely(pte_alloc(fe.vma->vm_mm, fe.pmd, fe.address)))
-		return VM_FAULT_OOM;
-	/*
-	 * If a huge pmd materialized under us just retry later.  Use
-	 * pmd_trans_unstable() instead of pmd_trans_huge() to ensure the pmd
-	 * didn't become pmd_trans_huge under us and then back to pmd_none, as
-	 * a result of MADV_DONTNEED running immediately after a huge pmd fault
-	 * in a different thread of this mm, in turn leading to a misleading
-	 * pmd_trans_huge() retval.  All we have to ensure is that it is a
-	 * regular pmd that we can walk with pte_offset_map() and we can do that
-	 * through an atomic read in C, which is what pmd_trans_unstable()
-	 * provides.
-	 */
-	if (unlikely(pmd_trans_unstable(fe.pmd) || pmd_devmap(*fe.pmd)))
-		return 0;
-	/*
-	 * A regular pmd is established and it can't morph into a huge pmd
-	 * from under us anymore at this point because we hold the mmap_sem
-	 * read mode and khugepaged takes it in write mode. So now it's
-	 * safe to run pte_offset_map().
-	 */
-	fe.pte = pte_offset_map(fe.pmd, fe.address);
-
 	return handle_pte_fault(&fe);
 }