[PATCH net-next v5 0/4] vsock/virtio/vhost: MSG_ZEROCOPY preparations

[PATCH net-next v5 0/4] vsock/virtio/vhost: MSG_ZEROCOPY preparations

[Arseniy Krasnov]

Hello,

this patchset is first of three parts of another big patchset for
MSG_ZEROCOPY flag support:
https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@sberdevices.ru/

During review of this series, Stefano Garzarella <sgarzare@redhat.com>
suggested to split it for three parts to simplify review and merging:

1) virtio and vhost updates (for fragged skbs) <--- this patchset
2) AF_VSOCK updates (allows to enable MSG_ZEROCOPY mode and read
   tx completions) and update for Documentation/.
3) Updates for tests and utils.

This series enables handling of fragged skbs in virtio and vhost parts.
Newly logic won't be triggered, because SO_ZEROCOPY options is still
impossible to enable at this moment (next bunch of patches from big
set above will enable it).

I've included changelog to some patches anyway, because there were some
comments during review of last big patchset from the link above.

Head for this patchset is 9d0cd5d25f7d45bce01bbb3193b54ac24b3a60f3

Link to v1:
https://lore.kernel.org/netdev/20230717210051.856388-1-AVKrasnov@sberdevices.ru/
Link to v2:
https://lore.kernel.org/netdev/20230718180237.3248179-1-AVKrasnov@sberdevices.ru/
Link to v3:
https://lore.kernel.org/netdev/20230720214245.457298-1-AVKrasnov@sberdevices.ru/
Link to v4:
https://lore.kernel.org/netdev/20230727222627.1895355-1-AVKrasnov@sberdevices.ru/

Changelog:
 v3 -> v4:
 * Patchset rebased and tested on new HEAD of net-next (see hash above).
 v4 -> v5:
 * See per-patch changelog after ---.

Arseniy Krasnov (4):
  vsock/virtio/vhost: read data from non-linear skb
  vsock/virtio: support to send non-linear skb
  vsock/virtio: non-linear skb handling for tap
  vsock/virtio: MSG_ZEROCOPY flag support

 drivers/vhost/vsock.c                   |  14 +-
 include/linux/virtio_vsock.h            |   6 +
 net/vmw_vsock/virtio_transport.c        |  74 +++++-
 net/vmw_vsock/virtio_transport_common.c | 300 ++++++++++++++++++------
 4 files changed, 313 insertions(+), 81 deletions(-)

-- 
2.25.1

[PATCH net-next v5 1/4] vsock/virtio/vhost: read data from non-linear skb

[Arseniy Krasnov]

This is preparation patch for MSG_ZEROCOPY support. It adds handling of
non-linear skbs by replacing direct calls of 'memcpy_to_msg()' with
'skb_copy_datagram_iter()'. Main advantage of the second one is that it
can handle paged part of the skb by using 'kmap()' on each page, but if
there are no pages in the skb, it behaves like simple copying to iov
iterator. This patch also adds new field to the control block of skb -
this value shows current offset in the skb to read next portion of data
(it doesn't matter linear it or not). Idea behind this field is that
'skb_copy_datagram_iter()' handles both types of skb internally - it
just needs an offset from which to copy data from the given skb. This
offset is incremented on each read from skb. This approach allows to
avoid special handling of non-linear skbs:
1) We can't call 'skb_pull()' on it, because it updates 'data' pointer.
2) We need to update 'data_len' also on each read from this skb.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 Changelog:
 v5(big patchset) -> v1:
  * Merge 'virtio_transport_common.c' and 'vhost/vsock.c' patches into
    this single patch.
  * Commit message update: grammar fix and remark that this patch is
    MSG_ZEROCOPY preparation.
  * Use 'min_t()' instead of comparison using '<>' operators.
 v1 -> v2:
  * R-b tag added.
 v3 -> v4:
  * R-b tag removed due to rebase:
    * Part for 'virtio_transport_stream_do_peek()' is changed.
    * Part for 'virtio_transport_seqpacket_do_peek()' is added.
  * Comments about sleep in 'memcpy_to_msg()' now describe sleep in
    'skb_copy_datagram_iter()'.

 drivers/vhost/vsock.c                   | 14 +++++++----
 include/linux/virtio_vsock.h            |  1 +
 net/vmw_vsock/virtio_transport_common.c | 32 +++++++++++++++----------
 3 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 817d377a3f36..8c917be32b5d 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		struct sk_buff *skb;
 		unsigned out, in;
 		size_t nbytes;
+		u32 frag_off;
 		int head;
 
 		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
@@ -156,7 +157,8 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		}
 
 		iov_iter_init(&iov_iter, ITER_DEST, &vq->iov[out], in, iov_len);
-		payload_len = skb->len;
+		frag_off = VIRTIO_VSOCK_SKB_CB(skb)->frag_off;
+		payload_len = skb->len - frag_off;
 		hdr = virtio_vsock_hdr(skb);
 
 		/* If the packet is greater than the space available in the
@@ -197,8 +199,10 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 			break;
 		}
 
-		nbytes = copy_to_iter(skb->data, payload_len, &iov_iter);
-		if (nbytes != payload_len) {
+		if (skb_copy_datagram_iter(skb,
+					   frag_off,
+					   &iov_iter,
+					   payload_len)) {
 			kfree_skb(skb);
 			vq_err(vq, "Faulted on copying pkt buf\n");
 			break;
@@ -212,13 +216,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		vhost_add_used(vq, head, sizeof(*hdr) + payload_len);
 		added = true;
 
-		skb_pull(skb, payload_len);
+		VIRTIO_VSOCK_SKB_CB(skb)->frag_off += payload_len;
 		total_len += payload_len;
 
 		/* If we didn't send all the payload we can requeue the packet
 		 * to send it with the next available buffer.
 		 */
-		if (skb->len > 0) {
+		if (VIRTIO_VSOCK_SKB_CB(skb)->frag_off < skb->len) {
 			hdr->flags |= cpu_to_le32(flags_to_restore);
 
 			/* We are queueing the same skb to handle
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index c58453699ee9..17dbb7176e37 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -12,6 +12,7 @@
 struct virtio_vsock_skb_cb {
 	bool reply;
 	bool tap_delivered;
+	u32 frag_off;
 };
 
 #define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb))
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 352d042b130b..0b6a89139810 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -364,9 +364,10 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 		spin_unlock_bh(&vvs->rx_lock);
 
 		/* sk_lock is held by caller so no one else can dequeue.
-		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 		 */
-		err = memcpy_to_msg(msg, skb->data, bytes);
+		err = skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->frag_off,
+					     &msg->msg_iter, bytes);
 		if (err)
 			goto out;
 
@@ -410,25 +411,27 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	while (total < len && !skb_queue_empty(&vvs->rx_queue)) {
 		skb = skb_peek(&vvs->rx_queue);
 
-		bytes = len - total;
-		if (bytes > skb->len)
-			bytes = skb->len;
+		bytes = min_t(size_t, len - total,
+			      skb->len - VIRTIO_VSOCK_SKB_CB(skb)->frag_off);
 
 		/* sk_lock is held by caller so no one else can dequeue.
-		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 		 */
 		spin_unlock_bh(&vvs->rx_lock);
 
-		err = memcpy_to_msg(msg, skb->data, bytes);
+		err = skb_copy_datagram_iter(skb,
+					     VIRTIO_VSOCK_SKB_CB(skb)->frag_off,
+					     &msg->msg_iter, bytes);
 		if (err)
 			goto out;
 
 		spin_lock_bh(&vvs->rx_lock);
 
 		total += bytes;
-		skb_pull(skb, bytes);
 
-		if (skb->len == 0) {
+		VIRTIO_VSOCK_SKB_CB(skb)->frag_off += bytes;
+
+		if (skb->len == VIRTIO_VSOCK_SKB_CB(skb)->frag_off) {
 			u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
 
 			virtio_transport_dec_rx_pkt(vvs, pkt_len);
@@ -492,9 +495,10 @@ virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
 			spin_unlock_bh(&vvs->rx_lock);
 
 			/* sk_lock is held by caller so no one else can dequeue.
-			 * Unlock rx_lock since memcpy_to_msg() may sleep.
+			 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 			 */
-			err = memcpy_to_msg(msg, skb->data, bytes);
+			err = skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->frag_off,
+						     &msg->msg_iter, bytes);
 			if (err)
 				return err;
 
@@ -553,11 +557,13 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 				int err;
 
 				/* sk_lock is held by caller so no one else can dequeue.
-				 * Unlock rx_lock since memcpy_to_msg() may sleep.
+				 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 				 */
 				spin_unlock_bh(&vvs->rx_lock);
 
-				err = memcpy_to_msg(msg, skb->data, bytes_to_copy);
+				err = skb_copy_datagram_iter(skb, 0,
+							     &msg->msg_iter,
+							     bytes_to_copy);
 				if (err) {
 					/* Copy of message failed. Rest of
 					 * fragments will be freed without copy.
-- 
2.25.1

Re: [PATCH net-next v5 1/4] vsock/virtio/vhost: read data from non-linear skb

[Paolo Abeni]

On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
> This is preparation patch for MSG_ZEROCOPY support. It adds handling of
> non-linear skbs by replacing direct calls of 'memcpy_to_msg()' with
> 'skb_copy_datagram_iter()'. Main advantage of the second one is that it
> can handle paged part of the skb by using 'kmap()' on each page, but if
> there are no pages in the skb, it behaves like simple copying to iov
> iterator. This patch also adds new field to the control block of skb -
> this value shows current offset in the skb to read next portion of data
> (it doesn't matter linear it or not). Idea behind this field is that
> 'skb_copy_datagram_iter()' handles both types of skb internally - it
> just needs an offset from which to copy data from the given skb. This
> offset is incremented on each read from skb. This approach allows to
> avoid special handling of non-linear skbs:
> 1) We can't call 'skb_pull()' on it, because it updates 'data' pointer.
> 2) We need to update 'data_len' also on each read from this skb.

It looks like the above sentence is a left-over from previous version
as, as this patch does not touch data_len. And I think it contradicts
the previous one, so it's a bit confusing.

> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
> ---
>  Changelog:
>  v5(big patchset) -> v1:
>   * Merge 'virtio_transport_common.c' and 'vhost/vsock.c' patches into
>     this single patch.
>   * Commit message update: grammar fix and remark that this patch is
>     MSG_ZEROCOPY preparation.
>   * Use 'min_t()' instead of comparison using '<>' operators.
>  v1 -> v2:
>   * R-b tag added.
>  v3 -> v4:
>   * R-b tag removed due to rebase:
>     * Part for 'virtio_transport_stream_do_peek()' is changed.
>     * Part for 'virtio_transport_seqpacket_do_peek()' is added.
>   * Comments about sleep in 'memcpy_to_msg()' now describe sleep in
>     'skb_copy_datagram_iter()'.
> 
>  drivers/vhost/vsock.c                   | 14 +++++++----
>  include/linux/virtio_vsock.h            |  1 +
>  net/vmw_vsock/virtio_transport_common.c | 32 +++++++++++++++----------
>  3 files changed, 29 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 817d377a3f36..8c917be32b5d 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>  		struct sk_buff *skb;
>  		unsigned out, in;
>  		size_t nbytes;
> +		u32 frag_off;

IMHO 'offset' would be a better name for both the variable and the CB
field, as it can points both inside the skb frags, linear part or frag
list.

Otherwise LGTM, thanks!

Paolo

Re: [PATCH net-next v5 1/4] vsock/virtio/vhost: read data from non-linear skb

[Arseniy Krasnov]

On 01.08.2023 16:11, Paolo Abeni wrote:
> On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
>> This is preparation patch for MSG_ZEROCOPY support. It adds handling of
>> non-linear skbs by replacing direct calls of 'memcpy_to_msg()' with
>> 'skb_copy_datagram_iter()'. Main advantage of the second one is that it
>> can handle paged part of the skb by using 'kmap()' on each page, but if
>> there are no pages in the skb, it behaves like simple copying to iov
>> iterator. This patch also adds new field to the control block of skb -
>> this value shows current offset in the skb to read next portion of data
>> (it doesn't matter linear it or not). Idea behind this field is that
>> 'skb_copy_datagram_iter()' handles both types of skb internally - it
>> just needs an offset from which to copy data from the given skb. This
>> offset is incremented on each read from skb. This approach allows to
>> avoid special handling of non-linear skbs:
>> 1) We can't call 'skb_pull()' on it, because it updates 'data' pointer.
>> 2) We need to update 'data_len' also on each read from this skb.
> 
> It looks like the above sentence is a left-over from previous version
> as, as this patch does not touch data_len. And I think it contradicts
> the previous one, so it's a bit confusing.

Yes, seems I need to rephrase it in the next version. I meant that with
approach introduced in this patch we don't need to check that skb is
linear of non-linear after reading data from it. Because otherwise:
1) In case of linear skb we will need to call 'skb_pull()' after reading
   data, to update 'data' pointer.
2) In case of non-linear skb we will need to update 'data_len' field after
   reading data, as this field shows amount of data in fragged part.

> 
>> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>> ---
>>  Changelog:
>>  v5(big patchset) -> v1:
>>   * Merge 'virtio_transport_common.c' and 'vhost/vsock.c' patches into
>>     this single patch.
>>   * Commit message update: grammar fix and remark that this patch is
>>     MSG_ZEROCOPY preparation.
>>   * Use 'min_t()' instead of comparison using '<>' operators.
>>  v1 -> v2:
>>   * R-b tag added.
>>  v3 -> v4:
>>   * R-b tag removed due to rebase:
>>     * Part for 'virtio_transport_stream_do_peek()' is changed.
>>     * Part for 'virtio_transport_seqpacket_do_peek()' is added.
>>   * Comments about sleep in 'memcpy_to_msg()' now describe sleep in
>>     'skb_copy_datagram_iter()'.
>>
>>  drivers/vhost/vsock.c                   | 14 +++++++----
>>  include/linux/virtio_vsock.h            |  1 +
>>  net/vmw_vsock/virtio_transport_common.c | 32 +++++++++++++++----------
>>  3 files changed, 29 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> index 817d377a3f36..8c917be32b5d 100644
>> --- a/drivers/vhost/vsock.c
>> +++ b/drivers/vhost/vsock.c
>> @@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>>  		struct sk_buff *skb;
>>  		unsigned out, in;
>>  		size_t nbytes;
>> +		u32 frag_off;
> 
> IMHO 'offset' would be a better name for both the variable and the CB
> field, as it can points both inside the skb frags, linear part or frag
> list.

Ack

> 
> Otherwise LGTM, thanks!
> 
> Paolo
> 

Thanks, Arseniy

[PATCH net-next v5 2/4] vsock/virtio: support to send non-linear skb

[Arseniy Krasnov]

For non-linear skb use its pages from fragment array as buffers in
virtio tx queue. These pages are already pinned by 'get_user_pages()'
during such skb creation.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
---
 Changelog:
 v2 -> v3:
  * Comment about 'page_to_virt()' is updated. I don't remove R-b,
    as this change is quiet small I guess.

 net/vmw_vsock/virtio_transport.c | 41 +++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index e95df847176b..7bbcc8093e51 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -100,7 +100,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
-		struct scatterlist hdr, buf, *sgs[2];
+		/* +1 is for packet header. */
+		struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
+		struct scatterlist bufs[MAX_SKB_FRAGS + 1];
 		int ret, in_sg = 0, out_sg = 0;
 		struct sk_buff *skb;
 		bool reply;
@@ -111,12 +113,39 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 		virtio_transport_deliver_tap_pkt(skb);
 		reply = virtio_vsock_skb_reply(skb);
+		sg_init_one(&bufs[out_sg], virtio_vsock_hdr(skb),
+			    sizeof(*virtio_vsock_hdr(skb)));
+		sgs[out_sg] = &bufs[out_sg];
+		out_sg++;
+
+		if (!skb_is_nonlinear(skb)) {
+			if (skb->len > 0) {
+				sg_init_one(&bufs[out_sg], skb->data, skb->len);
+				sgs[out_sg] = &bufs[out_sg];
+				out_sg++;
+			}
+		} else {
+			struct skb_shared_info *si;
+			int i;
+
+			si = skb_shinfo(skb);
+
+			for (i = 0; i < si->nr_frags; i++) {
+				skb_frag_t *skb_frag = &si->frags[i];
+				void *va;
 
-		sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
-		sgs[out_sg++] = &hdr;
-		if (skb->len > 0) {
-			sg_init_one(&buf, skb->data, skb->len);
-			sgs[out_sg++] = &buf;
+				/* We will use 'page_to_virt()' for the userspace page
+				 * here, because virtio or dma-mapping layers will call
+				 * 'virt_to_phys()' later to fill the buffer descriptor.
+				 * We don't touch memory at "virtual" address of this page.
+				 */
+				va = page_to_virt(skb_frag->bv_page);
+				sg_init_one(&bufs[out_sg],
+					    va + skb_frag->bv_offset,
+					    skb_frag->bv_len);
+				sgs[out_sg] = &bufs[out_sg];
+				out_sg++;
+			}
 		}
 
 		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
-- 
2.25.1

[PATCH net-next v5 3/4] vsock/virtio: non-linear skb handling for tap

[Arseniy Krasnov]

For tap device new skb is created and data from the current skb is
copied to it. This adds copying data from non-linear skb to new
the skb.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 31 ++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 0b6a89139810..de7b44675254 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -106,6 +106,27 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
 	return NULL;
 }
 
+static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb,
+						void *dst,
+						size_t len)
+{
+	struct iov_iter iov_iter = { 0 };
+	struct kvec kvec;
+	size_t to_copy;
+
+	kvec.iov_base = dst;
+	kvec.iov_len = len;
+
+	iov_iter.iter_type = ITER_KVEC;
+	iov_iter.kvec = &kvec;
+	iov_iter.nr_segs = 1;
+
+	to_copy = min_t(size_t, len, skb->len);
+
+	skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->frag_off,
+			       &iov_iter, to_copy);
+}
+
 /* Packet capture */
 static struct sk_buff *virtio_transport_build_skb(void *opaque)
 {
@@ -114,7 +135,6 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	struct af_vsockmon_hdr *hdr;
 	struct sk_buff *skb;
 	size_t payload_len;
-	void *payload_buf;
 
 	/* A packet could be split to fit the RX buffer, so we can retrieve
 	 * the payload length from the header and the buffer pointer taking
@@ -122,7 +142,6 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	 */
 	pkt_hdr = virtio_vsock_hdr(pkt);
 	payload_len = pkt->len;
-	payload_buf = pkt->data;
 
 	skb = alloc_skb(sizeof(*hdr) + sizeof(*pkt_hdr) + payload_len,
 			GFP_ATOMIC);
@@ -165,7 +184,13 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	skb_put_data(skb, pkt_hdr, sizeof(*pkt_hdr));
 
 	if (payload_len) {
-		skb_put_data(skb, payload_buf, payload_len);
+		if (skb_is_nonlinear(pkt)) {
+			void *data = skb_put(skb, payload_len);
+
+			virtio_transport_copy_nonlinear_skb(pkt, data, payload_len);
+		} else {
+			skb_put_data(skb, pkt->data, payload_len);
+		}
 	}
 
 	return skb;
-- 
2.25.1

[PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Arseniy Krasnov]

This adds handling of MSG_ZEROCOPY flag on transmission path: if this
flag is set and zerocopy transmission is possible (enabled in socket
options and transport allows zerocopy), then non-linear skb will be
created and filled with the pages of user's buffer. Pages of user's
buffer are locked in memory by 'get_user_pages()'. Second thing that
this patch does is replace type of skb owning: instead of calling
'skb_set_owner_sk_safe()' it calls 'skb_set_owner_w()'. Reason of this
change is that '__zerocopy_sg_from_iter()' increments 'sk_wmem_alloc'
of socket, so to decrease this field correctly proper skb destructor is
needed: 'sock_wfree()'. This destructor is set by 'skb_set_owner_w()'.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 Changelog:
 v5(big patchset) -> v1:
  * Refactorings of 'if' conditions.
  * Remove extra blank line.
  * Remove 'frag_off' field unneeded init.
  * Add function 'virtio_transport_fill_skb()' which fills both linear
    and non-linear skb with provided data.
 v1 -> v2:
  * Use original order of last four arguments in 'virtio_transport_alloc_skb()'.
 v2 -> v3:
  * Add new transport callback: 'msgzerocopy_check_iov'. It checks that
    provided 'iov_iter' with data could be sent in a zerocopy mode.
    If this callback is not set in transport - transport allows to send
    any 'iov_iter' in zerocopy mode. Otherwise - if callback returns 'true'
    then zerocopy is allowed. Reason of this callback is that in case of
    G2H transmission we insert whole skb to the tx virtio queue and such
    skb must fit to the size of the virtio queue to be sent in a single
    iteration (may be tx logic in 'virtio_transport.c' could be reworked
    as in vhost to support partial send of current skb). This callback
    will be enabled only for G2H path. For details pls see comment 
    'Check that tx queue...' below.
 v3 -> v4:
  * 'msgzerocopy_check_iov' moved from 'struct vsock_transport' to
    'struct virtio_transport' as it is virtio specific callback and
    never needed in other transports.
 v4 -> v5:
  * 'msgzerocopy_check_iov' renamed to 'can_msgzerocopy' and now it
    uses number of buffers to send as input argument. I think there is
    no need to pass iov to this callback (at least today, it is used only
    by guest side of virtio transport), because the only thing that this
    callback does is comparison of number of buffers to be inserted to
    the tx queue and size of this queue.
  * Remove any checks for type of current 'iov_iter' with payload (is it
    'iovec' or 'ubuf'). These checks left from the earlier versions where I
    didn't use already implemented kernel API which handles every type of
    'iov_iter'.

 include/linux/virtio_vsock.h            |   5 +
 net/vmw_vsock/virtio_transport.c        |  33 ++++
 net/vmw_vsock/virtio_transport_common.c | 245 ++++++++++++++++++------
 3 files changed, 225 insertions(+), 58 deletions(-)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 17dbb7176e37..bd47ced41c0d 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -160,6 +160,11 @@ struct virtio_transport {
 
 	/* Takes ownership of the packet */
 	int (*send_pkt)(struct sk_buff *skb);
+
+	/* Used in MSG_ZEROCOPY mode. Checks that provided data
+	 * could be transmitted with zerocopy mode.
+	 */
+	bool (*can_msgzerocopy)(int bufs_num);
 };
 
 ssize_t
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 7bbcc8093e51..eae7758dce56 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -442,6 +442,38 @@ static void virtio_vsock_rx_done(struct virtqueue *vq)
 	queue_work(virtio_vsock_workqueue, &vsock->rx_work);
 }
 
+static bool virtio_transport_can_msgzerocopy(int bufs_num)
+{
+	struct virtio_vsock *vsock;
+	bool res = false;
+
+	rcu_read_lock();
+
+	vsock = rcu_dereference(the_virtio_vsock);
+	if (vsock) {
+		struct virtqueue *vq = vsock->vqs[VSOCK_VQ_TX];
+
+		/* Check that tx queue is large enough to keep whole
+		 * data to send. This is needed, because when there is
+		 * not enough free space in the queue, current skb to
+		 * send will be reinserted to the head of tx list of
+		 * the socket to retry transmission later, so if skb
+		 * is bigger than whole queue, it will be reinserted
+		 * again and again, thus blocking other skbs to be sent.
+		 * Each page of the user provided buffer will be added
+		 * as a single buffer to the tx virtqueue, so compare
+		 * number of pages against maximum capacity of the queue.
+		 * +1 means buffer for the packet header.
+		 */
+		if (bufs_num + 1 <= vq->num_max)
+			res = true;
+	}
+
+	rcu_read_unlock();
+
+	return res;
+}
+
 static bool virtio_transport_seqpacket_allow(u32 remote_cid);
 
 static struct virtio_transport virtio_transport = {
@@ -491,6 +523,7 @@ static struct virtio_transport virtio_transport = {
 	},
 
 	.send_pkt = virtio_transport_send_pkt,
+	.can_msgzerocopy = virtio_transport_can_msgzerocopy,
 };
 
 static bool virtio_transport_seqpacket_allow(u32 remote_cid)
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index de7b44675254..1995f7f2e10c 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -37,73 +37,110 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
 	return container_of(t, struct virtio_transport, transport);
 }
 
-/* Returns a new packet on success, otherwise returns NULL.
- *
- * If NULL is returned, errp is set to a negative errno.
- */
-static struct sk_buff *
-virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
-			   size_t len,
-			   u32 src_cid,
-			   u32 src_port,
-			   u32 dst_cid,
-			   u32 dst_port)
-{
-	const size_t skb_len = VIRTIO_VSOCK_SKB_HEADROOM + len;
-	struct virtio_vsock_hdr *hdr;
-	struct sk_buff *skb;
-	void *payload;
-	int err;
+static bool virtio_transport_can_zcopy(struct virtio_vsock_pkt_info *info,
+				       size_t max_to_send)
+{
+	const struct virtio_transport *t_ops;
+	struct iov_iter *iov_iter;
 
-	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
-	if (!skb)
-		return NULL;
+	if (!info->msg)
+		return false;
 
-	hdr = virtio_vsock_hdr(skb);
-	hdr->type	= cpu_to_le16(info->type);
-	hdr->op		= cpu_to_le16(info->op);
-	hdr->src_cid	= cpu_to_le64(src_cid);
-	hdr->dst_cid	= cpu_to_le64(dst_cid);
-	hdr->src_port	= cpu_to_le32(src_port);
-	hdr->dst_port	= cpu_to_le32(dst_port);
-	hdr->flags	= cpu_to_le32(info->flags);
-	hdr->len	= cpu_to_le32(len);
+	iov_iter = &info->msg->msg_iter;
 
-	if (info->msg && len > 0) {
-		payload = skb_put(skb, len);
-		err = memcpy_from_msg(payload, info->msg, len);
-		if (err)
-			goto out;
+	if (iov_iter->iov_offset)
+		return false;
 
-		if (msg_data_left(info->msg) == 0 &&
-		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
-			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
+	/* We can't send whole iov. */
+	if (iov_iter->count > max_to_send)
+		return false;
 
-			if (info->msg->msg_flags & MSG_EOR)
-				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
-		}
+	/* Check that transport can send data in zerocopy mode. */
+	t_ops = virtio_transport_get_ops(info->vsk);
+
+	if (t_ops->can_msgzerocopy) {
+		int pages_in_iov = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
+		int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);
+
+		return t_ops->can_msgzerocopy(pages_to_send);
 	}
 
-	if (info->reply)
-		virtio_vsock_skb_set_reply(skb);
+	return true;
+}
 
-	trace_virtio_transport_alloc_pkt(src_cid, src_port,
-					 dst_cid, dst_port,
-					 len,
-					 info->type,
-					 info->op,
-					 info->flags);
+static int virtio_transport_init_zcopy_skb(struct vsock_sock *vsk,
+					   struct sk_buff *skb,
+					   struct msghdr *msg,
+					   bool zerocopy)
+{
+	struct ubuf_info *uarg;
 
-	if (info->vsk && !skb_set_owner_sk_safe(skb, sk_vsock(info->vsk))) {
-		WARN_ONCE(1, "failed to allocate skb on vsock socket with sk_refcnt == 0\n");
-		goto out;
+	if (msg->msg_ubuf) {
+		uarg = msg->msg_ubuf;
+		net_zcopy_get(uarg);
+	} else {
+		struct iov_iter *iter = &msg->msg_iter;
+		struct ubuf_info_msgzc *uarg_zc;
+
+		uarg = msg_zerocopy_realloc(sk_vsock(vsk),
+					    iter->count,
+					    NULL);
+		if (!uarg)
+			return -1;
+
+		uarg_zc = uarg_to_msgzc(uarg);
+		uarg_zc->zerocopy = zerocopy ? 1 : 0;
 	}
 
-	return skb;
+	skb_zcopy_init(skb, uarg);
 
-out:
-	kfree_skb(skb);
-	return NULL;
+	return 0;
+}
+
+static int virtio_transport_fill_skb(struct sk_buff *skb,
+				     struct virtio_vsock_pkt_info *info,
+				     size_t len,
+				     bool zcopy)
+{
+	if (zcopy) {
+		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
+					      &info->msg->msg_iter,
+					      len);
+	} else {
+		void *payload;
+		int err;
+
+		payload = skb_put(skb, len);
+		err = memcpy_from_msg(payload, info->msg, len);
+		if (err)
+			return -1;
+
+		if (msg_data_left(info->msg))
+			return 0;
+
+		return 0;
+	}
+}
+
+static void virtio_transport_init_hdr(struct sk_buff *skb,
+				      struct virtio_vsock_pkt_info *info,
+				      u32 src_cid,
+				      u32 src_port,
+				      u32 dst_cid,
+				      u32 dst_port,
+				      size_t len)
+{
+	struct virtio_vsock_hdr *hdr;
+
+	hdr = virtio_vsock_hdr(skb);
+	hdr->type	= cpu_to_le16(info->type);
+	hdr->op		= cpu_to_le16(info->op);
+	hdr->src_cid	= cpu_to_le64(src_cid);
+	hdr->dst_cid	= cpu_to_le64(dst_cid);
+	hdr->src_port	= cpu_to_le32(src_port);
+	hdr->dst_port	= cpu_to_le32(dst_port);
+	hdr->flags	= cpu_to_le32(info->flags);
+	hdr->len	= cpu_to_le32(len);
 }
 
 static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb,
@@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
 		return VIRTIO_VSOCK_TYPE_SEQPACKET;
 }
 
+static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
+						  struct virtio_vsock_pkt_info *info,
+						  size_t payload_len,
+						  bool zcopy,
+						  u32 src_cid,
+						  u32 src_port,
+						  u32 dst_cid,
+						  u32 dst_port)
+{
+	struct sk_buff *skb;
+	size_t skb_len;
+
+	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
+
+	if (!zcopy)
+		skb_len += payload_len;
+
+	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	virtio_transport_init_hdr(skb, info, src_cid, src_port,
+				  dst_cid, dst_port,
+				  payload_len);
+
+	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
+	 * owner of skb without check to update 'sk_wmem_alloc'.
+	 */
+	if (vsk)
+		skb_set_owner_w(skb, sk_vsock(vsk));
+
+	if (info->msg && payload_len > 0) {
+		int err;
+
+		err = virtio_transport_fill_skb(skb, info, payload_len, zcopy);
+		if (err)
+			goto out;
+
+		if (info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
+			struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
+
+			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
+
+			if (info->msg->msg_flags & MSG_EOR)
+				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
+		}
+	}
+
+	if (info->reply)
+		virtio_vsock_skb_set_reply(skb);
+
+	trace_virtio_transport_alloc_pkt(src_cid, src_port,
+					 dst_cid, dst_port,
+					 payload_len,
+					 info->type,
+					 info->op,
+					 info->flags);
+
+	return skb;
+out:
+	kfree_skb(skb);
+	return NULL;
+}
+
 /* This function can only be used on connecting/connected sockets,
  * since a socket assigned to a transport is required.
  *
@@ -222,10 +323,12 @@ static u16 virtio_transport_get_type(struct sock *sk)
 static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 					  struct virtio_vsock_pkt_info *info)
 {
+	u32 max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
 	u32 src_cid, src_port, dst_cid, dst_port;
 	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	u32 pkt_len = info->pkt_len;
+	bool can_zcopy = false;
 	u32 rest_len;
 	int ret;
 
@@ -254,15 +357,30 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
 		return pkt_len;
 
+	if (info->msg) {
+		/* If zerocopy is not enabled by 'setsockopt()', we behave as
+		 * there is no MSG_ZEROCOPY flag set.
+		 */
+		if (!sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY))
+			info->msg->msg_flags &= ~MSG_ZEROCOPY;
+
+		if (info->msg->msg_flags & MSG_ZEROCOPY)
+			can_zcopy = virtio_transport_can_zcopy(info, pkt_len);
+
+		if (can_zcopy)
+			max_skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE,
+					    (MAX_SKB_FRAGS * PAGE_SIZE));
+	}
+
 	rest_len = pkt_len;
 
 	do {
 		struct sk_buff *skb;
 		size_t skb_len;
 
-		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
+		skb_len = min(max_skb_len, rest_len);
 
-		skb = virtio_transport_alloc_skb(info, skb_len,
+		skb = virtio_transport_alloc_skb(vsk, info, skb_len, can_zcopy,
 						 src_cid, src_port,
 						 dst_cid, dst_port);
 		if (!skb) {
@@ -270,6 +388,17 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 			break;
 		}
 
+		/* This is last skb to send this portion of data. */
+		if (info->msg && info->msg->msg_flags & MSG_ZEROCOPY &&
+		    skb_len == rest_len && info->op == VIRTIO_VSOCK_OP_RW) {
+			if (virtio_transport_init_zcopy_skb(vsk, skb,
+							    info->msg,
+							    can_zcopy)) {
+				ret = -ENOMEM;
+				break;
+			}
+		}
+
 		virtio_transport_inc_tx_pkt(vvs, skb);
 
 		ret = t_ops->send_pkt(skb);
@@ -985,7 +1114,7 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
 	if (!t)
 		return -ENOTCONN;
 
-	reply = virtio_transport_alloc_skb(&info, 0,
+	reply = virtio_transport_alloc_skb(NULL, &info, 0, false,
 					   le64_to_cpu(hdr->dst_cid),
 					   le32_to_cpu(hdr->dst_port),
 					   le64_to_cpu(hdr->src_cid),
-- 
2.25.1

Re: [PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Paolo Abeni]

On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
> +static int virtio_transport_fill_skb(struct sk_buff *skb,
> +				     struct virtio_vsock_pkt_info *info,
> +				     size_t len,
> +				     bool zcopy)
> +{
> +	if (zcopy) {
> +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
> +					      &info->msg->msg_iter,
> +					      len);
> +	} else {


No need for an else statement after 'return'

> +		void *payload;
> +		int err;
> +
> +		payload = skb_put(skb, len);
> +		err = memcpy_from_msg(payload, info->msg, len);
> +		if (err)
> +			return -1;
> +
> +		if (msg_data_left(info->msg))
> +			return 0;
> +

This path does not update truesize, evem if it increases the skb len...

> +		return 0;
> +	}
> +}

[...]

> @@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
>  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>  }
>  
> +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
> +						  struct virtio_vsock_pkt_info *info,
> +						  size_t payload_len,
> +						  bool zcopy,
> +						  u32 src_cid,
> +						  u32 src_port,
> +						  u32 dst_cid,
> +						  u32 dst_port)
> +{
> +	struct sk_buff *skb;
> +	size_t skb_len;
> +
> +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
> +
> +	if (!zcopy)
> +		skb_len += payload_len;
> +
> +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
> +	if (!skb)
> +		return NULL;
> +
> +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
> +				  dst_cid, dst_port,
> +				  payload_len);
> +
> +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
> +	 * owner of skb without check to update 'sk_wmem_alloc'.
> +	 */
> +	if (vsk)
> +		skb_set_owner_w(skb, sk_vsock(vsk));

... which can lead to bad things(TM) if the skb goes trough some later
non trivial processing, due to the above skb_set_owner_w().

Additionally can be the following condition be true:

	vsk == NULL && (info->msg && payload_len > 0) && zcopy

???

If so it looks like skb can go through __zerocopy_sg_from_iter() even
without a prior skb_set_owner_w()...


Cheers,

Paolo

Re: [PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Arseniy Krasnov]

On 01.08.2023 16:34, Paolo Abeni wrote:
> On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
>> +static int virtio_transport_fill_skb(struct sk_buff *skb,
>> +				     struct virtio_vsock_pkt_info *info,
>> +				     size_t len,
>> +				     bool zcopy)
>> +{
>> +	if (zcopy) {
>> +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
>> +					      &info->msg->msg_iter,
>> +					      len);
>> +	} else {
> 
> 
> No need for an else statement after 'return'
> 
>> +		void *payload;
>> +		int err;
>> +
>> +		payload = skb_put(skb, len);
>> +		err = memcpy_from_msg(payload, info->msg, len);
>> +		if (err)
>> +			return -1;
>> +
>> +		if (msg_data_left(info->msg))
>> +			return 0;
>> +
> 
> This path does not update truesize, evem if it increases the skb len...

Thanks, I'll fix it.

> 
>> +		return 0;
>> +	}
>> +}
> 
> [...]
> 
>> @@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>>  }
>>  
>> +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
>> +						  struct virtio_vsock_pkt_info *info,
>> +						  size_t payload_len,
>> +						  bool zcopy,
>> +						  u32 src_cid,
>> +						  u32 src_port,
>> +						  u32 dst_cid,
>> +						  u32 dst_port)
>> +{
>> +	struct sk_buff *skb;
>> +	size_t skb_len;
>> +
>> +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
>> +
>> +	if (!zcopy)
>> +		skb_len += payload_len;
>> +
>> +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>> +	if (!skb)
>> +		return NULL;
>> +
>> +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
>> +				  dst_cid, dst_port,
>> +				  payload_len);
>> +
>> +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
>> +	 * owner of skb without check to update 'sk_wmem_alloc'.
>> +	 */
>> +	if (vsk)
>> +		skb_set_owner_w(skb, sk_vsock(vsk));
> 
> ... which can lead to bad things(TM) if the skb goes trough some later
> non trivial processing, due to the above skb_set_owner_w().
> 
> Additionally can be the following condition be true:
> 
> 	vsk == NULL && (info->msg && payload_len > 0) && zcopy
> 
> ???

No, vsk == NULL only when we reset connection, in that case both info->msg == NULL and payload_len == 0,
as this is control message without any data.

> 
> If so it looks like skb can go through __zerocopy_sg_from_iter() even
> without a prior skb_set_owner_w()...
> 
> 
> Cheers,
> 
> Paolo
>

Thanks, Arseniy
 

Re: [PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Paolo Abeni]

On Tue, 2023-08-01 at 16:36 +0300, Arseniy Krasnov wrote:
> 
> On 01.08.2023 16:34, Paolo Abeni wrote:
> > On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
> > > +static int virtio_transport_fill_skb(struct sk_buff *skb,
> > > +				     struct virtio_vsock_pkt_info *info,
> > > +				     size_t len,
> > > +				     bool zcopy)
> > > +{
> > > +	if (zcopy) {
> > > +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
> > > +					      &info->msg->msg_iter,
> > > +					      len);
> > > +	} else {
> > 
> > 
> > No need for an else statement after 'return'
> > 
> > > +		void *payload;
> > > +		int err;
> > > +
> > > +		payload = skb_put(skb, len);
> > > +		err = memcpy_from_msg(payload, info->msg, len);
> > > +		if (err)
> > > +			return -1;
> > > +
> > > +		if (msg_data_left(info->msg))
> > > +			return 0;
> > > +
> > 
> > This path does not update truesize, evem if it increases the skb len...
> 
> Thanks, I'll fix it.
> 
> > 
> > > +		return 0;
> > > +	}
> > > +}
> > 
> > [...]
> > 
> > > @@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
> > >  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
> > >  }
> > >  
> > > +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
> > > +						  struct virtio_vsock_pkt_info *info,
> > > +						  size_t payload_len,
> > > +						  bool zcopy,
> > > +						  u32 src_cid,
> > > +						  u32 src_port,
> > > +						  u32 dst_cid,
> > > +						  u32 dst_port)
> > > +{
> > > +	struct sk_buff *skb;
> > > +	size_t skb_len;
> > > +
> > > +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
> > > +
> > > +	if (!zcopy)
> > > +		skb_len += payload_len;
> > > +
> > > +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
> > > +	if (!skb)
> > > +		return NULL;
> > > +
> > > +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
> > > +				  dst_cid, dst_port,
> > > +				  payload_len);
> > > +
> > > +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
> > > +	 * owner of skb without check to update 'sk_wmem_alloc'.
> > > +	 */
> > > +	if (vsk)
> > > +		skb_set_owner_w(skb, sk_vsock(vsk));
> > 
> > ... which can lead to bad things(TM) if the skb goes trough some later
> > non trivial processing, due to the above skb_set_owner_w().
> > 
> > Additionally can be the following condition be true:
> > 
> > 	vsk == NULL && (info->msg && payload_len > 0) && zcopy
> > 
> > ???
> 
> No, vsk == NULL only when we reset connection, in that case both info->msg == NULL and payload_len == 0,
> as this is control message without any data.

Perhaps a comment with possibly even a WARN_ON_ONCE(!<the above>) could
help ;)

Thanks!

Paolo

Re: [PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Arseniy Krasnov]

On 01.08.2023 17:04, Paolo Abeni wrote:
> On Tue, 2023-08-01 at 16:36 +0300, Arseniy Krasnov wrote:
>>
>> On 01.08.2023 16:34, Paolo Abeni wrote:
>>> On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
>>>> +static int virtio_transport_fill_skb(struct sk_buff *skb,
>>>> +				     struct virtio_vsock_pkt_info *info,
>>>> +				     size_t len,
>>>> +				     bool zcopy)
>>>> +{
>>>> +	if (zcopy) {
>>>> +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
>>>> +					      &info->msg->msg_iter,
>>>> +					      len);
>>>> +	} else {
>>>
>>>
>>> No need for an else statement after 'return'
>>>
>>>> +		void *payload;
>>>> +		int err;
>>>> +
>>>> +		payload = skb_put(skb, len);
>>>> +		err = memcpy_from_msg(payload, info->msg, len);
>>>> +		if (err)
>>>> +			return -1;
>>>> +
>>>> +		if (msg_data_left(info->msg))
>>>> +			return 0;
>>>> +
>>>
>>> This path does not update truesize, evem if it increases the skb len...
>>
>> Thanks, I'll fix it.
>>
>>>
>>>> +		return 0;
>>>> +	}
>>>> +}
>>>
>>> [...]
>>>
>>>> @@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>>>  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>>>>  }
>>>>  
>>>> +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
>>>> +						  struct virtio_vsock_pkt_info *info,
>>>> +						  size_t payload_len,
>>>> +						  bool zcopy,
>>>> +						  u32 src_cid,
>>>> +						  u32 src_port,
>>>> +						  u32 dst_cid,
>>>> +						  u32 dst_port)
>>>> +{
>>>> +	struct sk_buff *skb;
>>>> +	size_t skb_len;
>>>> +
>>>> +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
>>>> +
>>>> +	if (!zcopy)
>>>> +		skb_len += payload_len;
>>>> +
>>>> +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>>>> +	if (!skb)
>>>> +		return NULL;
>>>> +
>>>> +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
>>>> +				  dst_cid, dst_port,
>>>> +				  payload_len);
>>>> +
>>>> +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
>>>> +	 * owner of skb without check to update 'sk_wmem_alloc'.
>>>> +	 */
>>>> +	if (vsk)
>>>> +		skb_set_owner_w(skb, sk_vsock(vsk));
>>>
>>> ... which can lead to bad things(TM) if the skb goes trough some later
>>> non trivial processing, due to the above skb_set_owner_w().
>>>
>>> Additionally can be the following condition be true:
>>>
>>> 	vsk == NULL && (info->msg && payload_len > 0) && zcopy
>>>
>>> ???
>>
>> No, vsk == NULL only when we reset connection, in that case both info->msg == NULL and payload_len == 0,
>> as this is control message without any data.
> 
> Perhaps a comment with possibly even a WARN_ON_ONCE(!<the above>) could
> help ;)

Ack

Thanks, Arseniy

> 
> Thanks!
> 
> Paolo
> 

Re: [PATCH net-next v5 4/4] vsock/virtio: MSG_ZEROCOPY flag support

[Arseniy Krasnov]

On 01.08.2023 16:34, Paolo Abeni wrote:
> On Sun, 2023-07-30 at 11:59 +0300, Arseniy Krasnov wrote:
>> +static int virtio_transport_fill_skb(struct sk_buff *skb,
>> +				     struct virtio_vsock_pkt_info *info,
>> +				     size_t len,
>> +				     bool zcopy)
>> +{
>> +	if (zcopy) {
>> +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
>> +					      &info->msg->msg_iter,
>> +					      len);
>> +	} else {
> 
> 
> No need for an else statement after 'return'
> 
>> +		void *payload;
>> +		int err;
>> +
>> +		payload = skb_put(skb, len);
>> +		err = memcpy_from_msg(payload, info->msg, len);
>> +		if (err)
>> +			return -1;
>> +
>> +		if (msg_data_left(info->msg))
>> +			return 0;
>> +
> 
> This path does not update truesize, evem if it increases the skb len...

Sorry, but what is potential problem here ? In this path I copy data from the user's
buffer to the linear skb (there is no fragged part in this case). I think 'truesize'
is constant in this case - it is SKB_TRUESIZE(length of skb buffer) - there is no need
to update it as 'truesize' does not show amount of data in skb, only real size of
skb's buffer.

For non-linear case, __zerocopy_sg_from_iter() always updates 'sk_wmem_alloc' of the
socket during iterating over frags array.

Also 'skb_set_owner_w()' is called before this code, thus setting 'sk_wmem_alloc' to the
'truesize' value of the skb.

Thanks, Arseniy

> 
>> +		return 0;
>> +	}
>> +}
> 
> [...]
> 
>> @@ -214,6 +251,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>>  }
>>  
>> +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
>> +						  struct virtio_vsock_pkt_info *info,
>> +						  size_t payload_len,
>> +						  bool zcopy,
>> +						  u32 src_cid,
>> +						  u32 src_port,
>> +						  u32 dst_cid,
>> +						  u32 dst_port)
>> +{
>> +	struct sk_buff *skb;
>> +	size_t skb_len;
>> +
>> +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
>> +
>> +	if (!zcopy)
>> +		skb_len += payload_len;
>> +
>> +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>> +	if (!skb)
>> +		return NULL;
>> +
>> +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
>> +				  dst_cid, dst_port,
>> +				  payload_len);
>> +
>> +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
>> +	 * owner of skb without check to update 'sk_wmem_alloc'.
>> +	 */
>> +	if (vsk)
>> +		skb_set_owner_w(skb, sk_vsock(vsk));
> 
> ... which can lead to bad things(TM) if the skb goes trough some later
> non trivial processing, due to the above skb_set_owner_w().
> 
> Additionally can be the following condition be true:
> 
> 	vsk == NULL && (info->msg && payload_len > 0) && zcopy
> 
> ???
> 
> If so it looks like skb can go through __zerocopy_sg_from_iter() even
> without a prior skb_set_owner_w()...
> 
> 
> Cheers,
> 
> Paolo
>