On 16.02.2023 17:09, Stefano Garzarella wrote:

On Mon, Feb 06, 2023 at 06:57:16AM +0000, Arseniy Krasnov wrote:

quoted

This adds copying to guest's virtio buffers from non-linear skbs. Such
skbs are created by protocol layer when MSG_ZEROCOPY flags is used.

Signed-off-by: Arseniy Krasnov <redacted>
---
drivers/vhost/vsock.c        | 56 ++++++++++++++++++++++++++++++++----
include/linux/virtio_vsock.h | 12 ++++++++
2 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 1f3b89c885cc..60b9cafa3e31 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -86,6 +86,44 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)

    return NULL;
}

+static int vhost_transport_copy_nonlinear_skb(struct sk_buff *skb,
+                          struct iov_iter *iov_iter,
+                          size_t len)
+{
+    size_t rest_len = len;
+
+    while (rest_len && virtio_vsock_skb_has_frags(skb)) {
+        struct bio_vec *curr_vec;
+        size_t curr_vec_end;
+        size_t to_copy;
+        int curr_frag;
+        int curr_offs;
+
+        curr_frag = VIRTIO_VSOCK_SKB_CB(skb)->curr_frag;
+        curr_offs = VIRTIO_VSOCK_SKB_CB(skb)->frag_off;
+        curr_vec = &skb_shinfo(skb)->frags[curr_frag];
+
+        curr_vec_end = curr_vec->bv_offset + curr_vec->bv_len;
+        to_copy = min(rest_len, (size_t)(curr_vec_end - curr_offs));
+
+        if (copy_page_to_iter(curr_vec->bv_page, curr_offs,
+                      to_copy, iov_iter) != to_copy)
+            return -1;
+
+        rest_len -= to_copy;
+        VIRTIO_VSOCK_SKB_CB(skb)->frag_off += to_copy;
+
+        if (VIRTIO_VSOCK_SKB_CB(skb)->frag_off == (curr_vec_end)) {
+            VIRTIO_VSOCK_SKB_CB(skb)->curr_frag++;
+            VIRTIO_VSOCK_SKB_CB(skb)->frag_off = 0;
+        }
+    }

Can it happen that we exit this loop and rest_len is not 0?

In this case, is it correct to decrement data_len by len?

I see

Thanks,
Stefano

quoted

+
+    skb->data_len -= len;
+
+    return 0;
+}
+
static void
vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
                struct vhost_virtqueue *vq)

@@ -197,11 +235,19 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,

            break;
        }

-        nbytes = copy_to_iter(skb->data, payload_len, &iov_iter);
-        if (nbytes != payload_len) {
-            kfree_skb(skb);
-            vq_err(vq, "Faulted on copying pkt buf\n");
-            break;
+        if (skb_is_nonlinear(skb)) {
+            if (vhost_transport_copy_nonlinear_skb(skb, &iov_iter,
+                                   payload_len)) {
+                vq_err(vq, "Faulted on copying pkt buf from page\n");
+                break;
+            }
+        } else {
+            nbytes = copy_to_iter(skb->data, payload_len, &iov_iter);
+            if (nbytes != payload_len) {
+                kfree_skb(skb);
+                vq_err(vq, "Faulted on copying pkt buf\n");
+                break;
+            }
        }

        /* Deliver to monitoring devices all packets that we

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 3f9c16611306..e7efdb78ce6e 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h

@@ -12,6 +12,10 @@

struct virtio_vsock_skb_cb {
    bool reply;
    bool tap_delivered;
+    /* Current fragment in 'frags' of skb. */
+    u32 curr_frag;
+    /* Offset from 0 in current fragment. */
+    u32 frag_off;
};

#define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb))

@@ -46,6 +50,14 @@ static inline void virtio_vsock_skb_clear_tap_delivered(struct sk_buff *skb)

    VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered = false;
}

+static inline bool virtio_vsock_skb_has_frags(struct sk_buff *skb)
+{
+    if (!skb_is_nonlinear(skb))
+        return false;
+
+    return VIRTIO_VSOCK_SKB_CB(skb)->curr_frag != skb_shinfo(skb)->nr_frags;
+}
+
static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
{
    u32 len;
-- 
2.25.1