1 files changed, 204 insertions, 17 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3edb759c5c7d..30e7709a5121 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -32,6 +32,7 @@
 #include <linux/hugetlb.h>
 #include <linux/hugetlb_cgroup.h>
 #include <linux/node.h>
+#include <linux/userfaultfd_k.h>
 #include "internal.h"
 
 int hugepages_treat_as_movable;
@@ -1773,23 +1774,32 @@ free:
 }
 
 /*
- * When releasing a hugetlb pool reservation, any surplus pages that were
- * allocated to satisfy the reservation must be explicitly freed if they were
- * never used.
- * Called with hugetlb_lock held.
+ * This routine has two main purposes:
+ * 1) Decrement the reservation count (resv_huge_pages) by the value passed
+ *    in unused_resv_pages.  This corresponds to the prior adjustments made
+ *    to the associated reservation map.
+ * 2) Free any unused surplus pages that may have been allocated to satisfy
+ *    the reservation.  As many as unused_resv_pages may be freed.
+ *
+ * Called with hugetlb_lock held.  However, the lock could be dropped (and
+ * reacquired) during calls to cond_resched_lock.  Whenever dropping the lock,
+ * we must make sure nobody else can claim pages we are in the process of
+ * freeing.  Do this by ensuring resv_huge_page always is greater than the
+ * number of huge pages we plan to free when dropping the lock.
  */
 static void return_unused_surplus_pages(struct hstate *h,
 					unsigned long unused_resv_pages)
 {
 	unsigned long nr_pages;
 
-	/* Uncommit the reservation */
-	h->resv_huge_pages -= unused_resv_pages;
-
 	/* Cannot return gigantic pages currently */
 	if (hstate_is_gigantic(h))
-		return;
+		goto out;
 
+	/*
+	 * Part (or even all) of the reservation could have been backed
+	 * by pre-allocated pages. Only free surplus pages.
+	 */
 	nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
 
 	/*
@@ -1799,12 +1809,22 @@ static void return_unused_surplus_pages(struct hstate *h,
 	 * when the nodes with surplus pages have no free pages.
 	 * free_pool_huge_page() will balance the the freed pages across the
 	 * on-line nodes with memory and will handle the hstate accounting.
+	 *
+	 * Note that we decrement resv_huge_pages as we free the pages.  If
+	 * we drop the lock, resv_huge_pages will still be sufficiently large
+	 * to cover subsequent pages we may free.
 	 */
 	while (nr_pages--) {
+		h->resv_huge_pages--;
+		unused_resv_pages--;
 		if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
-			break;
+			goto out;
 		cond_resched_lock(&hugetlb_lock);
 	}
+
+out:
+	/* Fully uncommit the reservation */
+	h->resv_huge_pages -= unused_resv_pages;
 }
 
 
@@ -3661,6 +3681,38 @@ retry:
 		size = i_size_read(mapping->host) >> huge_page_shift(h);
 		if (idx >= size)
 			goto out;
+
+		/*
+		 * Check for page in userfault range
+		 */
+		if (userfaultfd_missing(vma)) {
+			u32 hash;
+			struct vm_fault vmf = {
+				.vma = vma,
+				.address = address,
+				.flags = flags,
+				/*
+				 * Hard to debug if it ends up being
+				 * used by a callee that assumes
+				 * something about the other
+				 * uninitialized fields... same as in
+				 * memory.c
+				 */
+			};
+
+			/*
+			 * hugetlb_fault_mutex must be dropped before
+			 * handling userfault.  Reacquire after handling
+			 * fault to make calling code simpler.
+			 */
+			hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping,
+							idx, address);
+			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+			ret = handle_userfault(&vmf, VM_UFFD_MISSING);
+			mutex_lock(&hugetlb_fault_mutex_table[hash]);
+			goto out;
+		}
+
 		page = alloc_huge_page(vma, address, 0);
 		if (IS_ERR(page)) {
 			ret = PTR_ERR(page);
@@ -3929,10 +3981,113 @@ out_mutex:
 	return ret;
 }
 
+/*
+ * Used by userfaultfd UFFDIO_COPY.  Based on mcopy_atomic_pte with
+ * modifications for huge pages.
+ */
+int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
+			    pte_t *dst_pte,
+			    struct vm_area_struct *dst_vma,
+			    unsigned long dst_addr,
+			    unsigned long src_addr,
+			    struct page **pagep)
+{
+	int vm_shared = dst_vma->vm_flags & VM_SHARED;
+	struct hstate *h = hstate_vma(dst_vma);
+	pte_t _dst_pte;
+	spinlock_t *ptl;
+	int ret;
+	struct page *page;
+
+	if (!*pagep) {
+		ret = -ENOMEM;
+		page = alloc_huge_page(dst_vma, dst_addr, 0);
+		if (IS_ERR(page))
+			goto out;
+
+		ret = copy_huge_page_from_user(page,
+						(const void __user *) src_addr,
+						pages_per_huge_page(h), false);
+
+		/* fallback to copy_from_user outside mmap_sem */
+		if (unlikely(ret)) {
+			ret = -EFAULT;
+			*pagep = page;
+			/* don't free the page */
+			goto out;
+		}
+	} else {
+		page = *pagep;
+		*pagep = NULL;
+	}
+
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * preceding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__SetPageUptodate(page);
+	set_page_huge_active(page);
+
+	/*
+	 * If shared, add to page cache
+	 */
+	if (vm_shared) {
+		struct address_space *mapping = dst_vma->vm_file->f_mapping;
+		pgoff_t idx = vma_hugecache_offset(h, dst_vma, dst_addr);
+
+		ret = huge_add_to_page_cache(page, mapping, idx);
+		if (ret)
+			goto out_release_nounlock;
+	}
+
+	ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
+	spin_lock(ptl);
+
+	ret = -EEXIST;
+	if (!huge_pte_none(huge_ptep_get(dst_pte)))
+		goto out_release_unlock;
+
+	if (vm_shared) {
+		page_dup_rmap(page, true);
+	} else {
+		ClearPagePrivate(page);
+		hugepage_add_new_anon_rmap(page, dst_vma, dst_addr);
+	}
+
+	_dst_pte = make_huge_pte(dst_vma, page, dst_vma->vm_flags & VM_WRITE);
+	if (dst_vma->vm_flags & VM_WRITE)
+		_dst_pte = huge_pte_mkdirty(_dst_pte);
+	_dst_pte = pte_mkyoung(_dst_pte);
+
+	set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+
+	(void)huge_ptep_set_access_flags(dst_vma, dst_addr, dst_pte, _dst_pte,
+					dst_vma->vm_flags & VM_WRITE);
+	hugetlb_count_add(pages_per_huge_page(h), dst_mm);
+
+	/* No need to invalidate - it was non-present before */
+	update_mmu_cache(dst_vma, dst_addr, dst_pte);
+
+	spin_unlock(ptl);
+	if (vm_shared)
+		unlock_page(page);
+	ret = 0;
+out:
+	return ret;
+out_release_unlock:
+	spin_unlock(ptl);
+out_release_nounlock:
+	if (vm_shared)
+		unlock_page(page);
+	put_page(page);
+	goto out;
+}
+
 long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			 struct page **pages, struct vm_area_struct **vmas,
 			 unsigned long *position, unsigned long *nr_pages,
-			 long i, unsigned int flags)
+			 long i, unsigned int flags, int *nonblocking)
 {
 	unsigned long pfn_offset;
 	unsigned long vaddr = *position;
@@ -3995,16 +4150,43 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		    ((flags & FOLL_WRITE) &&
 		      !huge_pte_write(huge_ptep_get(pte)))) {
 			int ret;
+			unsigned int fault_flags = 0;
 
 			if (pte)
 				spin_unlock(ptl);
-			ret = hugetlb_fault(mm, vma, vaddr,
-				(flags & FOLL_WRITE) ? FAULT_FLAG_WRITE : 0);
-			if (!(ret & VM_FAULT_ERROR))
-				continue;
-
-			remainder = 0;
-			break;
+			if (flags & FOLL_WRITE)
+				fault_flags |= FAULT_FLAG_WRITE;
+			if (nonblocking)
+				fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+			if (flags & FOLL_NOWAIT)
+				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
+					FAULT_FLAG_RETRY_NOWAIT;
+			if (flags & FOLL_TRIED) {
+				VM_WARN_ON_ONCE(fault_flags &
+						FAULT_FLAG_ALLOW_RETRY);
+				fault_flags |= FAULT_FLAG_TRIED;
+			}
+			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);
+			if (ret & VM_FAULT_ERROR) {
+				remainder = 0;
+				break;
+			}
+			if (ret & VM_FAULT_RETRY) {
+				if (nonblocking)
+					*nonblocking = 0;
+				*nr_pages = 0;
+				/*
+				 * VM_FAULT_RETRY must not return an
+				 * error, it will return zero
+				 * instead.
+				 *
+				 * No need to update "position" as the
+				 * caller will not check it after
+				 * *nr_pages is set to 0.
+				 */
+				return i;
+			}
+			continue;
 		}
 
 		pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
@@ -4033,6 +4215,11 @@ same_page:
 		spin_unlock(ptl);
 	}
 	*nr_pages = remainder;
+	/*
+	 * setting position is actually required only if remainder is
+	 * not zero but it's faster not to add a "if (remainder)"
+	 * branch.
+	 */
 	*position = vaddr;
 
 	return i ? i : -EFAULT;