Re: [RFC PATCH v1 04/12] vhost/vsock: non-linear skb handling support

[Krasnov Arseniy <AVKrasnov@sberdevices.ru>]

On 16.02.2023 17:09, Stefano Garzarella wrote:
> On Mon, Feb 06, 2023 at 06:57:16AM +0000, Arseniy Krasnov wrote:
>> 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 <AVKrasnov@sberdevices.ru>
>> ---
>> 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
> 
>> +
>> +    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
>