Re: [PATCH net-next v9 6/6] vhost/net: Support VIRTIO_NET_F_HASH_REPORT

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2025/03/11 9:42, Jason Wang wrote:
> On Mon, Mar 10, 2025 at 3:04 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
>> On 2025/03/10 13:43, Jason Wang wrote:
>>> On Fri, Mar 7, 2025 at 7:02 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>>>
>>>> VIRTIO_NET_F_HASH_REPORT allows to report hash values calculated on the
>>>> host. When VHOST_NET_F_VIRTIO_NET_HDR is employed, it will report no
>>>> hash values (i.e., the hash_report member is always set to
>>>> VIRTIO_NET_HASH_REPORT_NONE). Otherwise, the values reported by the
>>>> underlying socket will be reported.
>>>>
>>>> VIRTIO_NET_F_HASH_REPORT requires VIRTIO_F_VERSION_1.
>>>>
>>>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>>>> Tested-by: Lei Yang <leiyang@redhat.com>
>>>> ---
>>>>    drivers/vhost/net.c | 49 +++++++++++++++++++++++++++++--------------------
>>>>    1 file changed, 29 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>>>> index b9b9e9d40951856d881d77ac74331d914473cd56..16b241b44f89820a42c302f3586ea6bb5e0d4289 100644
>>>> --- a/drivers/vhost/net.c
>>>> +++ b/drivers/vhost/net.c
>>>> @@ -73,6 +73,7 @@ enum {
>>>>           VHOST_NET_FEATURES = VHOST_FEATURES |
>>>>                            (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
>>>>                            (1ULL << VIRTIO_NET_F_MRG_RXBUF) |
>>>> +                        (1ULL << VIRTIO_NET_F_HASH_REPORT) |
>>>>                            (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
>>>>                            (1ULL << VIRTIO_F_RING_RESET)
>>>>    };
>>>> @@ -1097,9 +1098,11 @@ static void handle_rx(struct vhost_net *net)
>>>>                   .msg_controllen = 0,
>>>>                   .msg_flags = MSG_DONTWAIT,
>>>>           };
>>>> -       struct virtio_net_hdr hdr = {
>>>> -               .flags = 0,
>>>> -               .gso_type = VIRTIO_NET_HDR_GSO_NONE
>>>> +       struct virtio_net_hdr_v1_hash hdr = {
>>>> +               .hdr = {
>>>> +                       .flags = 0,
>>>> +                       .gso_type = VIRTIO_NET_HDR_GSO_NONE
>>>> +               }
>>>>           };
>>>>           size_t total_len = 0;
>>>>           int err, mergeable;
>>>> @@ -1110,7 +1113,6 @@ static void handle_rx(struct vhost_net *net)
>>>>           bool set_num_buffers;
>>>>           struct socket *sock;
>>>>           struct iov_iter fixup;
>>>> -       __virtio16 num_buffers;
>>>>           int recv_pkts = 0;
>>>>
>>>>           mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_RX);
>>>> @@ -1191,30 +1193,30 @@ static void handle_rx(struct vhost_net *net)
>>>>                           vhost_discard_vq_desc(vq, headcount);
>>>>                           continue;
>>>>                   }
>>>> +               hdr.hdr.num_buffers = cpu_to_vhost16(vq, headcount);
>>>>                   /* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
>>>>                   if (unlikely(vhost_hlen)) {
>>>> -                       if (copy_to_iter(&hdr, sizeof(hdr),
>>>> -                                        &fixup) != sizeof(hdr)) {
>>>> +                       if (copy_to_iter(&hdr, vhost_hlen,
>>>> +                                        &fixup) != vhost_hlen) {
>>>>                                   vq_err(vq, "Unable to write vnet_hdr "
>>>>                                          "at addr %p\n", vq->iov->iov_base);
>>>>                                   goto out;
>>>
>>> Is this an "issue" specific to RSS/HASH? If it's not, we need a separate patch.
>>>
>>> Honestly, I'm not sure if it's too late to fix this.
>>
>> There is nothing wrong with the current implementation.
> 
> Note that I meant the vhost_hlen part, and the current code is tricky.
> 
> The comment said:
> 
> """
> /* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
> """
> 
> So it tries to only offer virtio_net_hdr even if vhost_hlen is the set
> to mrg_rxbuf len.
> 
> And this patch changes this behaviour.

mrg_rxbuf only adds the num_buffers field, which is always set for 
mrg_rxbuf.

The num_buffers was not set for VIRTIO_F_VERSION_1 in the past, but this 
was also fixed with commit a3b9c053d82a ("vhost/net: Set num_buffers for 
virtio 1.0")

So there is no behavioral change for existing features with this patch.

Regards,
Akihiko Odaki

> 
> Thanks
> 
>> The current
>> implementation fills the header with zero except num_buffers, which it
>> fills some real value. This functionality is working fine with
>> VIRTIO_NET_F_MRG_RXBUF and VIRTIO_F_VERSION_1, which change the header size.
>>
>> Now I'm adding VIRTIO_NET_F_HASH_REPORT and it adds the hash_report
>> field, which also needs to be initialized with zero, so I'm making sure
>> vhost_net will also initialize it.
>>
>> Regards,
>> Akihiko Odaki
>>
>>>
>>> Others look fine.
>>>
>>> Thanks
>>>
>>
>