[RFC PATCH v2 2/8] vhost/vsock: rework packet allocation logic

[Arseniy Krasnov <AVKrasnov@sberdevices.ru>]

For packets received from virtio RX queue, use buddy
allocator instead of 'kmalloc()' to be able to insert
such pages to user provided vma. Single call to
'copy_from_iter()' replaced with per-page loop.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 drivers/vhost/vsock.c | 81 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 69 insertions(+), 12 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index e6c9d41db1de..0dc2229f18f7 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -58,6 +58,7 @@ struct vhost_vsock {
 
 	u32 guest_cid;
 	bool seqpacket_allow;
+	bool zerocopy_rx_on;
 };
 
 static u32 vhost_transport_get_local_cid(void)
@@ -357,6 +358,7 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
 		      unsigned int out, unsigned int in)
 {
 	struct virtio_vsock_pkt *pkt;
+	struct vhost_vsock *vsock;
 	struct iov_iter iov_iter;
 	size_t nbytes;
 	size_t len;
@@ -393,20 +395,75 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
 		return NULL;
 	}
 
-	pkt->buf = kmalloc(pkt->len, GFP_KERNEL);
-	if (!pkt->buf) {
-		kfree(pkt);
-		return NULL;
-	}
-
 	pkt->buf_len = pkt->len;
+	vsock = container_of(vq->dev, struct vhost_vsock, dev);
 
-	nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
-	if (nbytes != pkt->len) {
-		vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
-		       pkt->len, nbytes);
-		virtio_transport_free_pkt(pkt);
-		return NULL;
+	if (!vsock->zerocopy_rx_on) {
+		pkt->buf = kmalloc(pkt->len, GFP_KERNEL);
+
+		if (!pkt->buf) {
+			kfree(pkt);
+			return NULL;
+		}
+
+		pkt->slab_buf = true;
+		nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
+		if (nbytes != pkt->len) {
+			vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
+				pkt->len, nbytes);
+			virtio_transport_free_pkt(pkt);
+			return NULL;
+		}
+	} else {
+		struct page *buf_page;
+		ssize_t pkt_len;
+		int page_idx;
+
+		/* This creates memory overrun, as we allocate
+		 * at least one page for each packet.
+		 */
+		buf_page = alloc_pages(GFP_KERNEL, get_order(pkt->len));
+
+		if (buf_page == NULL) {
+			kfree(pkt);
+			return NULL;
+		}
+
+		pkt->buf = page_to_virt(buf_page);
+
+		page_idx = 0;
+		pkt_len = pkt->len;
+
+		/* As allocated pages are not mapped, process
+		 * pages one by one.
+		 */
+		while (pkt_len > 0) {
+			void *mapped;
+			size_t to_copy;
+
+			mapped = kmap(buf_page + page_idx);
+
+			if (mapped == NULL) {
+				virtio_transport_free_pkt(pkt);
+				return NULL;
+			}
+
+			to_copy = min(pkt_len, ((ssize_t)PAGE_SIZE));
+
+			nbytes = copy_from_iter(mapped, to_copy, &iov_iter);
+			if (nbytes != to_copy) {
+				vq_err(vq, "Expected %zu byte payload, got %zu bytes\n",
+				       to_copy, nbytes);
+				kunmap(mapped);
+				virtio_transport_free_pkt(pkt);
+				return NULL;
+			}
+
+			kunmap(mapped);
+
+			pkt_len -= to_copy;
+			page_idx++;
+		}
 	}
 
 	return pkt;
-- 
2.25.1