process_vm_access: switch to copy_page_to_iter/iov_iter_copy_from_user

... rather than open-coding those.  As a side benefit, we get much saner
loop calling those; we can just feed entire pages, instead of the "copy
would span the iovec boundary, let's do it in two loop iterations" mess.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 1e3c811..70ec315 100644 (file)
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -51,13 +51,11 @@ static int process_vm_rw_pages(struct task_struct *task,
                               ssize_t *bytes_copied)
 {
        int pages_pinned;
-       void *target_kaddr;
        int pgs_copied = 0;
        int j;
        int ret;
        ssize_t bytes_to_copy;
        ssize_t rc = 0;
-       const struct iovec *iov = iter->iov;
 
        *bytes_copied = 0;
 
@@ -75,77 +73,34 @@ static int process_vm_rw_pages(struct task_struct *task,
 
        /* Do the copy for each page */
        for (pgs_copied = 0;
-            (pgs_copied < nr_pages_to_copy) && iter->nr_segs;
+            (pgs_copied < nr_pages_to_copy) && iov_iter_count(iter);
             pgs_copied++) {
-               /* Make sure we have a non zero length iovec */
-               while (iter->nr_segs && iov->iov_len == 0) {
-                       iov++;
-                       iter->nr_segs--;
+               struct page *page = process_pages[pgs_copied];
+               bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset, len);
+
+               if (vm_write) {
+                       if (bytes_to_copy > iov_iter_count(iter))
+                               bytes_to_copy = iov_iter_count(iter);
+                       ret = iov_iter_copy_from_user(page,
+                                       iter, start_offset, bytes_to_copy);
+                       iov_iter_advance(iter, ret);
+                       set_page_dirty_lock(page);
+               } else {
+                       ret = copy_page_to_iter(page, start_offset,
+                                       bytes_to_copy, iter);
                }
-               if (!iter->nr_segs)
-                       break;
-
-               /*
-                * Will copy smallest of:
-                * - bytes remaining in page
-                * - bytes remaining in destination iovec
-                */
-               bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
-                                     len - *bytes_copied);
-               bytes_to_copy = min_t(ssize_t, bytes_to_copy,
-                                     iov->iov_len
-                                     - iter->iov_offset);
-
-               target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;
-
-               if (vm_write)
-                       ret = copy_from_user(target_kaddr,
-                                            iov->iov_base
-                                            + iter->iov_offset,
-                                            bytes_to_copy);
-               else
-                       ret = copy_to_user(iov->iov_base
-                                          + iter->iov_offset,
-                                          target_kaddr, bytes_to_copy);
-               kunmap(process_pages[pgs_copied]);
-               if (ret) {
-                       *bytes_copied += bytes_to_copy - ret;
-                       pgs_copied++;
+               *bytes_copied += ret;
+               len -= ret;
+               if (ret < bytes_to_copy && iov_iter_count(iter)) {
                        rc = -EFAULT;
-                       goto end;
-               }
-               *bytes_copied += bytes_to_copy;
-               iter->iov_offset += bytes_to_copy;
-               if (iter->iov_offset == iov->iov_len) {
-                       /*
-                        * Need to copy remaining part of page into the
-                        * next iovec if there are any bytes left in page
-                        */
-                       iter->nr_segs--;
-                       iov++;
-                       iter->iov_offset = 0;
-                       start_offset = (start_offset + bytes_to_copy)
-                               % PAGE_SIZE;
-                       if (start_offset)
-                               pgs_copied--;
-               } else {
-                       start_offset = 0;
+                       break;
                }
+               start_offset = 0;
        }
 
 end:
-       if (vm_write) {
-               for (j = 0; j < pages_pinned; j++) {
-                       if (j < pgs_copied)
-                               set_page_dirty_lock(process_pages[j]);
-                       put_page(process_pages[j]);
-               }
-       } else {
-               for (j = 0; j < pages_pinned; j++)
-                       put_page(process_pages[j]);
-       }
-
-       iter->iov = iov;
+       for (j = 0; j < pages_pinned; j++)
+               put_page(process_pages[j]);
        return rc;
 }
 
@@ -194,7 +149,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
                return 0;
        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 
-       while ((nr_pages_copied < nr_pages) && iter->nr_segs) {
+       while ((nr_pages_copied < nr_pages) && iov_iter_count(iter)) {
                nr_pages_to_copy = min(nr_pages - nr_pages_copied,
                                       max_pages_per_loop);
 
@@ -303,7 +258,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
                goto put_task_struct;
        }
 
-       for (i = 0; i < riovcnt && iter->nr_segs; i++) {
+       for (i = 0; i < riovcnt && iov_iter_count(iter); i++) {
                rc = process_vm_rw_single_vec(
                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
                        iter, process_pages, mm, task, vm_write,