[RFC PATCH 1/6] mm/memory: add copy_huge_page_from_user for hugetlb userfaultfd support

[Mike Kravetz]

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.

Signed-off-by: Mike Kravetz <mike.krav...@oracle.com>
---
 include/linux/mm.h |  3 +++
 mm/memory.c        | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0510282..7ecc7e7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2355,6 +2355,9 @@ extern void clear_huge_page(struct page *page,
 extern void copy_user_huge_page(struct page *dst, struct page *src,
                                unsigned long addr, struct vm_area_struct *vma,
                                unsigned int pages_per_huge_page);
+extern long copy_huge_page_from_user(const void __user *usr_src,
+                               struct page *dst_page,
+                               unsigned int pages_per_huge_page);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 extern struct page_ext_operations debug_guardpage_ops;
diff --git a/mm/memory.c b/mm/memory.c
index 19584b9..c44ddad 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3970,6 +3970,28 @@ 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(const void __user *usr_src,
+                               struct page *dst_page,
+                               unsigned int pages_per_huge_page)
+{
+       void *src = (void *)usr_src;
+       void *page_kaddr;
+       long i, rc = 0;
+
+       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);
+               if (rc)
+                       break;
+
+               cond_resched();
+       }
+       return rc;
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if USE_SPLIT_PTE_PTLOCKS && ALLOC_SPLIT_PTLOCKS
-- 
2.4.11