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>

4 files changed, 53 insertions, 28 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 13d16a2b7623..1cec28d20583 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;
diff --git a/mm/mremap.c b/mm/mremap.c
index 8779928d6a70..8233b0105c82 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -252,7 +252,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 static unsigned long move_vma(struct vm_area_struct *vma,
                 unsigned long old_addr, unsigned long old_len,
                 unsigned long new_len, unsigned long new_addr,
-                bool *locked, struct vm_userfaultfd_ctx *uf)
+                bool *locked, struct vm_userfaultfd_ctx *uf,
+                struct list_head *uf_unmap)
 {
         struct mm_struct *mm = vma->vm_mm;
         struct vm_area_struct *new_vma;
@@ -341,7 +342,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
         if (unlikely(vma->vm_flags & VM_PFNMAP))
                 untrack_pfn_moved(vma);
 
-        if (do_munmap(mm, old_addr, old_len) < 0) {
+        if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
                 /* OOM: unable to split vma, just get accounts right */
                 vm_unacct_memory(excess >> PAGE_SHIFT);
                 excess = 0;
@@ -417,7 +418,8 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
 
 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
                 unsigned long new_addr, unsigned long new_len, bool *locked,
-                struct vm_userfaultfd_ctx *uf)
+                struct vm_userfaultfd_ctx *uf,
+                struct list_head *uf_unmap)
 {
         struct mm_struct *mm = current->mm;
         struct vm_area_struct *vma;
@@ -435,12 +437,12 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
         if (addr + old_len > new_addr && new_addr + new_len > addr)
                 goto out;
 
-        ret = do_munmap(mm, new_addr, new_len);
+        ret = do_munmap(mm, new_addr, new_len, NULL);
         if (ret)
                 goto out;
 
         if (old_len >= new_len) {
-                ret = do_munmap(mm, addr+new_len, old_len - new_len);
+                ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
                 if (ret && old_len != new_len)
                         goto out;
                 old_len = new_len;
@@ -462,7 +464,8 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
         if (offset_in_page(ret))
                 goto out1;
 
-        ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf);
+        ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf,
+                       uf_unmap);
         if (!(offset_in_page(ret)))
                 goto out;
 out1:
@@ -502,6 +505,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
         unsigned long charged = 0;
         bool locked = false;
         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
+        LIST_HEAD(uf_unmap);
 
         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
                 return ret;
@@ -528,7 +532,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 
         if (flags & MREMAP_FIXED) {
                 ret = mremap_to(addr, old_len, new_addr, new_len,
-                                &locked, &uf);
+                                &locked, &uf, &uf_unmap);
                 goto out;
         }
 
@@ -538,7 +542,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
          * do_munmap does all the needed commit accounting
          */
         if (old_len >= new_len) {
-                ret = do_munmap(mm, addr+new_len, old_len - new_len);
+                ret = do_munmap(mm, addr+new_len, old_len - new_len, &uf_unmap);
                 if (ret && old_len != new_len)
                         goto out;
                 ret = addr;
@@ -598,7 +602,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
                 }
 
                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
-                               &locked, &uf);
+                               &locked, &uf, &uf_unmap);
         }
 out:
         if (offset_in_page(ret)) {
@@ -609,5 +613,6 @@ out:
         if (locked && new_len > old_len)
                 mm_populate(new_addr + old_len, new_len - old_len);
         mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
+        userfaultfd_unmap_complete(mm, &uf_unmap);
         return ret;
 }
diff --git a/mm/nommu.c b/mm/nommu.c
index 215c62296028..fe9f4fa4a7a7 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1205,7 +1205,8 @@ unsigned long do_mmap(struct file *file,
                         unsigned long flags,
                         vm_flags_t vm_flags,
                         unsigned long pgoff,
-                        unsigned long *populate)
+                        unsigned long *populate,
+                        struct list_head *uf)
 {
         struct vm_area_struct *vma;
         struct vm_region *region;
@@ -1577,7 +1578,7 @@ static int shrink_vma(struct mm_struct *mm,
  * - under NOMMU conditions the chunk to be unmapped must be backed by a single
  *   VMA, though it need not cover the whole VMA
  */
-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)
 {
         struct vm_area_struct *vma;
         unsigned long end;
@@ -1643,7 +1644,7 @@ int vm_munmap(unsigned long addr, size_t len)
         int ret;
 
         down_write(&mm->mmap_sem);
-        ret = do_munmap(mm, addr, len);
+        ret = do_munmap(mm, addr, len, NULL);
         up_write(&mm->mmap_sem);
         return ret;
 }
diff --git a/mm/util.c b/mm/util.c
index 3cb2164f4099..b8f538863b5a 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -11,6 +11,7 @@
 #include <linux/mman.h>
 #include <linux/hugetlb.h>
 #include <linux/vmalloc.h>
+#include <linux/userfaultfd_k.h>
 
 #include <asm/sections.h>
 #include <linux/uaccess.h>
@@ -297,14 +298,16 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
         unsigned long ret;
         struct mm_struct *mm = current->mm;
         unsigned long populate;
+        LIST_HEAD(uf);
 
         ret = security_mmap_file(file, prot, flag);
         if (!ret) {
                 if (down_write_killable(&mm->mmap_sem))
                         return -EINTR;
                 ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,
-                                    &populate);
+                                    &populate, &uf);
                 up_write(&mm->mmap_sem);
+                userfaultfd_unmap_complete(mm, &uf);
                 if (populate)
                         mm_populate(ret, populate);
         }