tls: Generalize zerocopy_from_iter

Refactor zerocopy_from_iter to take arguments for pages and size,
such that it can be used for both tx and rx. RX will also support
zerocopy direct to output iter, as long as the full message can
be copied at once (a large enough userspace buffer was provided).

Signed-off-by: Dave Watson <davejwatson@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_sw.c

@@ -226,23 +226,24 @@ static int tls_sw_push_pending_record(struct sock *sk, int flags)
 }
 
 static int zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
-			      int length)
+			      int length, int *pages_used,
+			      unsigned int *size_used,
+			      struct scatterlist *to, int to_max_pages,
+			      bool charge)
 {
-	struct tls_context *tls_ctx = tls_get_ctx(sk);
-	struct tls_sw_context *ctx = tls_sw_ctx(tls_ctx);
 	struct page *pages[MAX_SKB_FRAGS];
 
 	size_t offset;
 	ssize_t copied, use;
 	int i = 0;
-	unsigned int size = ctx->sg_plaintext_size;
-	int num_elem = ctx->sg_plaintext_num_elem;
+	unsigned int size = *size_used;
+	int num_elem = *pages_used;
 	int rc = 0;
 	int maxpages;
 
 	while (length > 0) {
 		i = 0;
-		maxpages = ARRAY_SIZE(ctx->sg_plaintext_data) - num_elem;
+		maxpages = to_max_pages - num_elem;
 		if (maxpages == 0) {
 			rc = -EFAULT;
 			goto out;
@@ -262,10 +263,11 @@ static int zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
 		while (copied) {
 			use = min_t(int, copied, PAGE_SIZE - offset);
 
-			sg_set_page(&ctx->sg_plaintext_data[num_elem],
+			sg_set_page(&to[num_elem],
 				    pages[i], use, offset);
-			sg_unmark_end(&ctx->sg_plaintext_data[num_elem]);
-			sk_mem_charge(sk, use);
+			sg_unmark_end(&to[num_elem]);
+			if (charge)
+				sk_mem_charge(sk, use);
 
 			offset = 0;
 			copied -= use;
@@ -276,8 +278,9 @@ static int zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
 	}
 
 out:
-	ctx->sg_plaintext_size = size;
-	ctx->sg_plaintext_num_elem = num_elem;
+	*size_used = size;
+	*pages_used = num_elem;
+
 	return rc;
 }
 
@@ -374,7 +377,11 @@ alloc_encrypted:
 
 		if (full_record || eor) {
 			ret = zerocopy_from_iter(sk, &msg->msg_iter,
-						 try_to_copy);
+				try_to_copy, &ctx->sg_plaintext_num_elem,
+				&ctx->sg_plaintext_size,
+				ctx->sg_plaintext_data,
+				ARRAY_SIZE(ctx->sg_plaintext_data),
+				true);
 			if (ret)
 				goto fallback_to_reg_send;