userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support

userfaultfd UFFDIO_COPY allows user level code to copy data to a page at
fault time.  The data is copied from user space to a newly allocated
huge page.  The new routine copy_huge_page_from_user performs this copy.

Link: http://lkml.kernel.org/r/20161216144821.5183-17-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.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 Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index ececdc4a2892..4ade940d105c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4152,6 +4152,31 @@ void copy_user_huge_page(struct page *dst, struct page *src,
                 copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma);
         }
 }
+
+long copy_huge_page_from_user(struct page *dst_page,
+                                const void __user *usr_src,
+                                unsigned int pages_per_huge_page)
+{
+        void *src = (void *)usr_src;
+        void *page_kaddr;
+        unsigned long i, rc = 0;
+        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);
+                rc = copy_from_user(page_kaddr,
+                                (const void __user *)(src + i * PAGE_SIZE),
+                                PAGE_SIZE);
+                kunmap_atomic(page_kaddr);
+
+                ret_val -= (PAGE_SIZE - rc);
+                if (rc)
+                        break;
+
+                cond_resched();
+        }
+        return ret_val;
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if USE_SPLIT_PTE_PTLOCKS && ALLOC_SPLIT_PTLOCKS