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

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Date:   Fri, 3 Jun 2022 05:33:04 +0000
From:   Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>,
        Krasnov Arseniy <oxffffaa@...il.com>
Subject: [RFC PATCH v2 2/8] vhost/vsock: rework packet allocation logic

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@...rdevices.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