userfaultfd: mfill_atomic(): remove retry logic

Since __mfill_atomic_pte() handles the retry for both anonymous and shmem,
there is no need to retry copying the date from the userspace in the loop
in mfill_atomic().

Drop the retry logic from mfill_atomic().

[[email protected]: remove safety measure of not returning ENOENT from _copy]
  Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andrei Vagin <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: David Hildenbrand (Arm) <[email protected]>
Cc: Harry Yoo <[email protected]>
Cc: Harry Yoo (Oracle) <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes (Oracle) <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Nikita Kalyazin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Carlier <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/userfaultfd.c

@@ -29,7 +29,6 @@ struct mfill_state {
 	struct vm_area_struct *vma;
 	unsigned long src_addr;
 	unsigned long dst_addr;
-	struct folio *folio;
 	pmd_t *pmd;
 };
 
@@ -531,9 +530,6 @@ err_filemap_remove:
 		ops->filemap_remove(folio, state->vma);
 err_folio_put:
 	folio_put(folio);
-	/* Don't return -ENOENT so that our caller won't retry */
-	if (ret == -ENOENT)
-		ret = -EFAULT;
 	return ret;
 }
 
@@ -899,7 +895,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 	VM_WARN_ON_ONCE(src_start + len <= src_start);
 	VM_WARN_ON_ONCE(dst_start + len <= dst_start);
 
-retry:
 	err = mfill_get_vma(&state);
 	if (err)
 		goto out;
@@ -926,26 +921,6 @@ retry:
 		err = mfill_atomic_pte(&state);
 		cond_resched();
 
-		if (unlikely(err == -ENOENT)) {
-			void *kaddr;
-
-			mfill_put_vma(&state);
-			VM_WARN_ON_ONCE(!state.folio);
-
-			kaddr = kmap_local_folio(state.folio, 0);
-			err = copy_from_user(kaddr,
-					     (const void __user *)state.src_addr,
-					     PAGE_SIZE);
-			kunmap_local(kaddr);
-			if (unlikely(err)) {
-				err = -EFAULT;
-				goto out;
-			}
-			flush_dcache_folio(state.folio);
-			goto retry;
-		} else
-			VM_WARN_ON_ONCE(state.folio);
-
 		if (!err) {
 			state.dst_addr += PAGE_SIZE;
 			state.src_addr += PAGE_SIZE;
@@ -960,8 +935,6 @@ retry:
 
 	mfill_put_vma(&state);
 out:
-	if (state.folio)
-		folio_put(state.folio);
 	VM_WARN_ON_ONCE(copied < 0);
 	VM_WARN_ON_ONCE(err > 0);
 	VM_WARN_ON_ONCE(!copied && !err);