userfaultfd: shmem: add shmem_mfill_zeropage_pte for userfaultfd support

shmem_mfill_zeropage_pte is the low level routine that implements the
userfaultfd UFFDIO_ZEROPAGE command.  Since for shmem mappings zero
pages are always allocated and accounted, the new method is a slight
extension of the existing shmem_mcopy_atomic_pte.

Link: http://lkml.kernel.org/r/1497939652-16528-4-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Hugh Dickins <hughd@google.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>

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index a7d6bd2..b6c3540 100644 (file)
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -137,9 +137,15 @@ extern int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
                                  unsigned long dst_addr,
                                  unsigned long src_addr,
                                  struct page **pagep);
+extern int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
+                                   pmd_t *dst_pmd,
+                                   struct vm_area_struct *dst_vma,
+                                   unsigned long dst_addr);
 #else
 #define shmem_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma, dst_addr, \
                               src_addr, pagep)        ({ BUG(); 0; })
+#define shmem_mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma, \
+                                dst_addr)      ({ BUG(); 0; })
 #endif
 
 #endif

diff --git a/mm/shmem.c b/mm/shmem.c
index b7d84c4..64bdc91 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2207,12 +2207,13 @@ bool shmem_mapping(struct address_space *mapping)
        return mapping->a_ops == &shmem_aops;
 }
 
-int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
-                          pmd_t *dst_pmd,
-                          struct vm_area_struct *dst_vma,
-                          unsigned long dst_addr,
-                          unsigned long src_addr,
-                          struct page **pagep)
+static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
+                                 pmd_t *dst_pmd,
+                                 struct vm_area_struct *dst_vma,
+                                 unsigned long dst_addr,
+                                 unsigned long src_addr,
+                                 bool zeropage,
+                                 struct page **pagep)
 {
        struct inode *inode = file_inode(dst_vma->vm_file);
        struct shmem_inode_info *info = SHMEM_I(inode);
@@ -2235,17 +2236,22 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
                if (!page)
                        goto out_unacct_blocks;
 
-               page_kaddr = kmap_atomic(page);
-               ret = copy_from_user(page_kaddr, (const void __user *)src_addr,
-                                    PAGE_SIZE);
-               kunmap_atomic(page_kaddr);
-
-               /* fallback to copy_from_user outside mmap_sem */
-               if (unlikely(ret)) {
-                       *pagep = page;
-                       shmem_inode_unacct_blocks(inode, 1);
-                       /* don't free the page */
-                       return -EFAULT;
+               if (!zeropage) {        /* mcopy_atomic */
+                       page_kaddr = kmap_atomic(page);
+                       ret = copy_from_user(page_kaddr,
+                                            (const void __user *)src_addr,
+                                            PAGE_SIZE);
+                       kunmap_atomic(page_kaddr);
+
+                       /* fallback to copy_from_user outside mmap_sem */
+                       if (unlikely(ret)) {
+                               *pagep = page;
+                               shmem_inode_unacct_blocks(inode, 1);
+                               /* don't free the page */
+                               return -EFAULT;
+                       }
+               } else {                /* mfill_zeropage_atomic */
+                       clear_highpage(page);
                }
        } else {
                page = *pagep;
@@ -2311,6 +2317,28 @@ out_unacct_blocks:
        goto out;
 }
 
+int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
+                          pmd_t *dst_pmd,
+                          struct vm_area_struct *dst_vma,
+                          unsigned long dst_addr,
+                          unsigned long src_addr,
+                          struct page **pagep)
+{
+       return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
+                                     dst_addr, src_addr, false, pagep);
+}
+
+int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
+                            pmd_t *dst_pmd,
+                            struct vm_area_struct *dst_vma,
+                            unsigned long dst_addr)
+{
+       struct page *page = NULL;
+
+       return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
+                                     dst_addr, 0, true, &page);
+}
+
 #ifdef CONFIG_TMPFS
 static const struct inode_operations shmem_symlink_inode_operations;
 static const struct inode_operations shmem_short_symlink_operations;