userfaultfd: non-cooperative: add event for memory unmaps

When a non-cooperative userfaultfd monitor copies pages in the
background, it may encounter regions that were already unmapped.
Addition of UFFD_EVENT_UNMAP allows the uffd monitor to track precisely
changes in the virtual memory layout.

Since there might be different uffd contexts for the affected VMAs, we
first should create a temporary representation for the unmap event for
each uffd context and then notify them one by one to the appropriate
userfault file descriptors.

The event notification occurs after the mmap_sem has been released.

[arnd@arndb.de: fix nommu build]
  Link: http://lkml.kernel.org/r/20170203165141.3665284-1-arnd@arndb.de
[mhocko@suse.com: fix nommu build]
  Link: http://lkml.kernel.org/r/20170202091503.GA22823@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/1485542673-24387-3-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 15 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 13d16a2..1cec28d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -176,7 +176,7 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
 	return next;
 }
 
-static int do_brk(unsigned long addr, unsigned long len);
+static int do_brk(unsigned long addr, unsigned long len, struct list_head *uf);
 
 SYSCALL_DEFINE1(brk, unsigned long, brk)
 {
@@ -185,6 +185,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 	struct mm_struct *mm = current->mm;
 	unsigned long min_brk;
 	bool populate;
+	LIST_HEAD(uf);
 
 	if (down_write_killable(&mm->mmap_sem))
 		return -EINTR;
@@ -222,7 +223,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 
 	/* Always allow shrinking brk. */
 	if (brk <= mm->brk) {
-		if (!do_munmap(mm, newbrk, oldbrk-newbrk))
+		if (!do_munmap(mm, newbrk, oldbrk-newbrk, &uf))
 			goto set_brk;
 		goto out;
 	}
@@ -232,13 +233,14 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 		goto out;
 
 	/* Ok, looks good - let it rip. */
-	if (do_brk(oldbrk, newbrk-oldbrk) < 0)
+	if (do_brk(oldbrk, newbrk-oldbrk, &uf) < 0)
 		goto out;
 
 set_brk:
 	mm->brk = brk;
 	populate = newbrk > oldbrk && (mm->def_flags & VM_LOCKED) != 0;
 	up_write(&mm->mmap_sem);
+	userfaultfd_unmap_complete(mm, &uf);
 	if (populate)
 		mm_populate(oldbrk, newbrk - oldbrk);
 	return brk;
@@ -1304,7 +1306,8 @@ static inline int mlock_future_check(struct mm_struct *mm,
 unsigned long do_mmap(struct file *file, unsigned long addr,
 			unsigned long len, unsigned long prot,
 			unsigned long flags, vm_flags_t vm_flags,
-			unsigned long pgoff, unsigned long *populate)
+			unsigned long pgoff, unsigned long *populate,
+			struct list_head *uf)
 {
 	struct mm_struct *mm = current->mm;
 	int pkey = 0;
@@ -1447,7 +1450,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 			vm_flags |= VM_NORESERVE;
 	}
 
-	addr = mmap_region(file, addr, len, vm_flags, pgoff);
+	addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
 	if (!IS_ERR_VALUE(addr) &&
 	    ((vm_flags & VM_LOCKED) ||
 	     (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
@@ -1583,7 +1586,8 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
 }
 
 unsigned long mmap_region(struct file *file, unsigned long addr,
-		unsigned long len, vm_flags_t vm_flags, unsigned long pgoff)
+		unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
+		struct list_head *uf)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
@@ -1609,7 +1613,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	/* Clear old maps */
 	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
 			      &rb_parent)) {
-		if (do_munmap(mm, addr, len))
+		if (do_munmap(mm, addr, len, uf))
 			return -ENOMEM;
 	}
 
@@ -2579,7 +2583,8 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
  * work.  This now handles partial unmappings.
  * Jeremy Fitzhardinge <jeremy@goop.org>
  */
-int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
+int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
+	      struct list_head *uf)
 {
 	unsigned long end;
 	struct vm_area_struct *vma, *prev, *last;
@@ -2603,6 +2608,13 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
 	if (vma->vm_start >= end)
 		return 0;
 
+	if (uf) {
+		int error = userfaultfd_unmap_prep(vma, start, end, uf);
+
+		if (error)
+			return error;
+	}
+
 	/*
 	 * If we need to split any vma, do it now to save pain later.
 	 *
@@ -2668,12 +2680,14 @@ int vm_munmap(unsigned long start, size_t len)
 {
 	int ret;
 	struct mm_struct *mm = current->mm;
+	LIST_HEAD(uf);
 
 	if (down_write_killable(&mm->mmap_sem))
 		return -EINTR;
 
-	ret = do_munmap(mm, start, len);
+	ret = do_munmap(mm, start, len, &uf);
 	up_write(&mm->mmap_sem);
+	userfaultfd_unmap_complete(mm, &uf);
 	return ret;
 }
 EXPORT_SYMBOL(vm_munmap);
@@ -2773,7 +2787,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 
 	file = get_file(vma->vm_file);
 	ret = do_mmap_pgoff(vma->vm_file, start, size,
-			prot, flags, pgoff, &populate);
+			prot, flags, pgoff, &populate, NULL);
 	fput(file);
 out:
 	up_write(&mm->mmap_sem);
@@ -2799,7 +2813,7 @@ static inline void verify_mm_writelocked(struct mm_struct *mm)
  *  anonymous maps.  eventually we may be able to do some
  *  brk-specific accounting here.
  */
-static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
+static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long flags, struct list_head *uf)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
@@ -2838,7 +2852,7 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long
 	 */
 	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
 			      &rb_parent)) {
-		if (do_munmap(mm, addr, len))
+		if (do_munmap(mm, addr, len, uf))
 			return -ENOMEM;
 	}
 
@@ -2885,9 +2899,9 @@ out:
 	return 0;
 }
 
-static int do_brk(unsigned long addr, unsigned long len)
+static int do_brk(unsigned long addr, unsigned long len, struct list_head *uf)
 {
-	return do_brk_flags(addr, len, 0);
+	return do_brk_flags(addr, len, 0, uf);
 }
 
 int vm_brk_flags(unsigned long addr, unsigned long len, unsigned long flags)
@@ -2895,13 +2909,15 @@ int vm_brk_flags(unsigned long addr, unsigned long len, unsigned long flags)
 	struct mm_struct *mm = current->mm;
 	int ret;
 	bool populate;
+	LIST_HEAD(uf);
 
 	if (down_write_killable(&mm->mmap_sem))
 		return -EINTR;
 
-	ret = do_brk_flags(addr, len, flags);
+	ret = do_brk_flags(addr, len, flags, &uf);
 	populate = ((mm->def_flags & VM_LOCKED) != 0);
 	up_write(&mm->mmap_sem);
+	userfaultfd_unmap_complete(mm, &uf);
 	if (populate && !ret)
 		mm_populate(addr, len);
 	return ret;