userfaultfd: hugetlbfs: fix __mcopy_atomic_hugetlb retry/error processing

The new routine copy_huge_page_from_user() uses kmap_atomic() to map
PAGE_SIZE pages.  However, this prevents page faults in the subsequent
call to copy_from_user().  This is OK in the case where the routine is
copied with mmap_sema held.  However, in another case we want to allow
page faults.  So, add a new argument allow_pagefault to indicate if the
routine should allow page faults.

[dan.carpenter@oracle.com: unmap the correct pointer]
  Link: http://lkml.kernel.org/r/20170113082608.GA3548@mwanda
[akpm@linux-foundation.org: kunmap() takes a page*, per Hugh]
Link: http://lkml.kernel.org/r/20161216144821.5183-20-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 3 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 4ade940d105c..d7676a68c80a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4155,7 +4155,8 @@ void copy_user_huge_page(struct page *dst, struct page *src,
 
 long copy_huge_page_from_user(struct page *dst_page,
                                 const void __user *usr_src,
-                                unsigned int pages_per_huge_page)
+                                unsigned int pages_per_huge_page,
+                                bool allow_pagefault)
 {
         void *src = (void *)usr_src;
         void *page_kaddr;
@@ -4163,11 +4164,17 @@ long copy_huge_page_from_user(struct page *dst_page,
         unsigned long ret_val = pages_per_huge_page * PAGE_SIZE;
 
         for (i = 0; i < pages_per_huge_page; i++) {
-                page_kaddr = kmap_atomic(dst_page + i);
+                if (allow_pagefault)
+                        page_kaddr = kmap(dst_page + i);
+                else
+                        page_kaddr = kmap_atomic(dst_page + i);
                 rc = copy_from_user(page_kaddr,
                                 (const void __user *)(src + i * PAGE_SIZE),
                                 PAGE_SIZE);
-                kunmap_atomic(page_kaddr);
+                if (allow_pagefault)
+                        kunmap(dst_page + i);
+                else
+                        kunmap_atomic(page_kaddr);
 
                 ret_val -= (PAGE_SIZE - rc);
                 if (rc)