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Message-ID: <9850943f-9ace-f4e2-edfb-aea9ff6c08e0@sberdevices.ru>
Date:   Tue, 18 Jul 2023 17:10:16 +0300
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Subject: Re: [PATCH net-next v1 4/4] vsock/virtio: MSG_ZEROCOPY flag support
To:     Stefano Garzarella <sgarzare@redhat.com>
CC:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        <kvm@vger.kernel.org>, <virtualization@lists.linux-foundation.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kernel@sberdevices.ru>, <oxffffaa@gmail.com>
References: <20230717210051.856388-1-AVKrasnov@sberdevices.ru>
 <20230717210051.856388-5-AVKrasnov@sberdevices.ru>
 <k7rovmw7abzkwhngbqwgg74qgkcvq2ggygo46y6skkxnchgqcj@7yabz52oh4sr>
Content-Language: en-US
From:   Arseniy Krasnov <avkrasnov@sberdevices.ru>
In-Reply-To: <k7rovmw7abzkwhngbqwgg74qgkcvq2ggygo46y6skkxnchgqcj@7yabz52oh4sr>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 18.07.2023 16:51, Stefano Garzarella wrote:
> On Tue, Jul 18, 2023 at 12:00:51AM +0300, Arseniy Krasnov wrote:
>> This adds handling of MSG_ZEROCOPY flag on transmission path: if this
>> flag is set and zerocopy transmission is possible, 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.
>>
>> net/vmw_vsock/virtio_transport_common.c | 260 ++++++++++++++++++------
>> 1 file changed, 197 insertions(+), 63 deletions(-)
>>
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 26a4d10da205..1fb0a0f694c6 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -37,73 +37,115 @@ 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)
>> +{
>> +    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;
>> +    /* Data is simple buffer. */
>> +    if (iter_is_ubuf(iov_iter))
>> +        return true;
>>
>> -        if (msg_data_left(info->msg) == 0 &&
>> -            info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
>> -            hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>> +    if (!iter_is_iovec(iov_iter))
>> +        return false;
>>
>> -            if (info->msg->msg_flags & MSG_EOR)
>> -                hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>> -        }
>> +    if (iov_iter->iov_offset)
>> +        return false;
>> +
>> +    /* We can't send whole iov. */
>> +    if (iov_iter->count > max_to_send)
>> +        return false;
>> +
>> +    return true;
>> +}
>> +
>> +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 (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;
>> +        int len;
>> +
>> +        /* Only ITER_IOVEC or ITER_UBUF are allowed and
>> +         * checked before.
>> +         */
>> +        if (iter_is_iovec(iter))
>> +            len = iov_length(iter->__iov, iter->nr_segs);
>> +        else
>> +            len = iter->count;
>> +
>> +        uarg = msg_zerocopy_realloc(sk_vsock(vsk),
>> +                        len,
>> +                        NULL);
>> +        if (!uarg)
>> +            return -1;
>> +
>> +        uarg_zc = uarg_to_msgzc(uarg);
>> +        uarg_zc->zerocopy = zerocopy ? 1 : 0;
>>     }
>>
>> -    if (info->reply)
>> -        virtio_vsock_skb_set_reply(skb);
>> +    skb_zcopy_init(skb, uarg);
>>
>> -    trace_virtio_transport_alloc_pkt(src_cid, src_port,
>> -                     dst_cid, dst_port,
>> -                     len,
>> -                     info->type,
>> -                     info->op,
>> -                     info->flags);
>> +    return 0;
>> +}
>>
>> -    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;
>> +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;
>>     }
>> +}
>>
>> -    return skb;
>> +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;
>>
>> -out:
>> -    kfree_skb(skb);
>> -    return NULL;
>> +    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 +256,70 @@ 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 dst_cid,
>> +                          u32 dst_port,
>> +                          u32 src_cid,
>> +                          u32 src_port)
> 
> Before this patch the order of dst_* and src_* fields were reversed
> for virtio_transport_alloc_skb(), why are we changing it?
> 
> I think putting them back as before (and following the same ordering in
> the new functions as well) makes the patch easier to review and the code
> easier to maintain.

Yes, exactly! I'll fix it. Seems I just didn't pay attention on this during
coding...

Thanks, Arseniy

> 
> Thanks,
> Stefano
> 
>> +{
>> +    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 +328,12 @@ 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;
>>
>> @@ -254,22 +362,48 @@ 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,
>> -                         src_cid, src_port,
>> -                         dst_cid, dst_port);
>> +        skb = virtio_transport_alloc_skb(vsk, info, skb_len, can_zcopy,
>> +                         dst_cid, dst_port,
>> +                         src_cid, src_port);
>>         if (!skb) {
>>             ret = -ENOMEM;
>>             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);
>> @@ -934,11 +1068,11 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
>>     if (!t)
>>         return -ENOTCONN;
>>
>> -    reply = virtio_transport_alloc_skb(&info, 0,
>> -                       le64_to_cpu(hdr->dst_cid),
>> -                       le32_to_cpu(hdr->dst_port),
>> +    reply = virtio_transport_alloc_skb(NULL, &info, 0, false,
>>                        le64_to_cpu(hdr->src_cid),
>> -                       le32_to_cpu(hdr->src_port));
>> +                       le32_to_cpu(hdr->src_port),
>> +                       le64_to_cpu(hdr->dst_cid),
>> +                       le32_to_cpu(hdr->dst_port));
>>     if (!reply)
>>         return -ENOMEM;
>>
>> -- 
>> 2.25.1
>>
>