io_uring: add io_pin_pages() helper

Abstract this out from io_sqe_buffer_register() so we can use it
elsewhere too without duplicating this code.

No intended functional changes in this patch.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -9845,30 +9845,18 @@ static int io_buffer_account_pin(struct io_ring_ctx *ctx, struct page **pages,
 	return ret;
 }
 
-static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
-				  struct io_mapped_ubuf **pimu,
-				  struct page **last_hpage)
+static struct page **io_pin_pages(unsigned long ubuf, unsigned long len,
+				  int *npages)
 {
-	struct io_mapped_ubuf *imu = NULL;
+	unsigned long start, end, nr_pages;
 	struct vm_area_struct **vmas = NULL;
 	struct page **pages = NULL;
-	unsigned long off, start, end, ubuf;
-	size_t size;
-	int ret, pret, nr_pages, i;
-
-	if (!iov->iov_base) {
-		*pimu = ctx->dummy_ubuf;
-		return 0;
-	}
+	int i, pret, ret = -ENOMEM;
 
-	ubuf = (unsigned long) iov->iov_base;
-	end = (ubuf + iov->iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	end = (ubuf + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	start = ubuf >> PAGE_SHIFT;
 	nr_pages = end - start;
 
-	*pimu = NULL;
-	ret = -ENOMEM;
-
 	pages = kvmalloc_array(nr_pages, sizeof(struct page *), GFP_KERNEL);
 	if (!pages)
 		goto done;
@@ -9878,10 +9866,6 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	if (!vmas)
 		goto done;
 
-	imu = kvmalloc(struct_size(imu, bvec, nr_pages), GFP_KERNEL);
-	if (!imu)
-		goto done;
-
 	ret = 0;
 	mmap_read_lock(current->mm);
 	pret = pin_user_pages(ubuf, nr_pages, FOLL_WRITE | FOLL_LONGTERM,
@@ -9899,6 +9883,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 				break;
 			}
 		}
+		*npages = nr_pages;
 	} else {
 		ret = pret < 0 ? pret : -EFAULT;
 	}
@@ -9912,14 +9897,53 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 			unpin_user_pages(pages, pret);
 		goto done;
 	}
+	ret = 0;
+done:
+	kvfree(vmas);
+	if (ret < 0) {
+		kvfree(pages);
+		pages = ERR_PTR(ret);
+	}
+	return pages;
+}
 
-	ret = io_buffer_account_pin(ctx, pages, pret, imu, last_hpage);
+static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
+				  struct io_mapped_ubuf **pimu,
+				  struct page **last_hpage)
+{
+	struct io_mapped_ubuf *imu = NULL;
+	struct page **pages = NULL;
+	unsigned long off;
+	size_t size;
+	int ret, nr_pages, i;
+
+	if (!iov->iov_base) {
+		*pimu = ctx->dummy_ubuf;
+		return 0;
+	}
+
+	*pimu = NULL;
+	ret = -ENOMEM;
+
+	pages = io_pin_pages((unsigned long) iov->iov_base, iov->iov_len,
+				&nr_pages);
+	if (IS_ERR(pages)) {
+		ret = PTR_ERR(pages);
+		pages = NULL;
+		goto done;
+	}
+
+	imu = kvmalloc(struct_size(imu, bvec, nr_pages), GFP_KERNEL);
+	if (!imu)
+		goto done;
+
+	ret = io_buffer_account_pin(ctx, pages, nr_pages, imu, last_hpage);
 	if (ret) {
-		unpin_user_pages(pages, pret);
+		unpin_user_pages(pages, nr_pages);
 		goto done;
 	}
 
-	off = ubuf & ~PAGE_MASK;
+	off = (unsigned long) iov->iov_base & ~PAGE_MASK;
 	size = iov->iov_len;
 	for (i = 0; i < nr_pages; i++) {
 		size_t vec_len;
@@ -9932,8 +9956,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 		size -= vec_len;
 	}
 	/* store original address for later verification */
-	imu->ubuf = ubuf;
-	imu->ubuf_end = ubuf + iov->iov_len;
+	imu->ubuf = (unsigned long) iov->iov_base;
+	imu->ubuf_end = imu->ubuf + iov->iov_len;
 	imu->nr_bvecs = nr_pages;
 	*pimu = imu;
 	ret = 0;
@@ -9941,7 +9965,6 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	if (ret)
 		kvfree(imu);
 	kvfree(pages);
-	kvfree(vmas);
 	return ret;
 }