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

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Message-ID: <2e550452-a716-4c3f-9d5a-3882d2c9912a@daynix.com>
Date: Mon, 10 Mar 2025 16:04:43 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Jonathan Corbet <corbet@....net>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kvm@...r.kernel.org,
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
 Yuri Benditovich <yuri.benditovich@...nix.com>,
 Andrew Melnychenko <andrew@...nix.com>,
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com,
 Lei Yang <leiyang@...hat.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next v9 6/6] vhost/net: Support
 VIRTIO_NET_F_HASH_REPORT

On 2025/03/10 13:43, Jason Wang wrote:
> On Fri, Mar 7, 2025 at 7:02 PM Akihiko Odaki <akihiko.odaki@...nix.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@...nix.com>
>> Tested-by: Lei Yang <leiyang@...hat.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. 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
>