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

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

On 2025/03/17 10:15, Jason Wang wrote:
> On Wed, Mar 12, 2025 at 1:59 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
>> On 2025/03/12 12:36, Jason Wang wrote:
>>> On Tue, Mar 11, 2025 at 2:24 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>>>
>>>> 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.
>>>
>>> I meant this part.
>>>
>>>>>>> +                       if (copy_to_iter(&hdr, vhost_hlen,
>>>>>>> +                                        &fixup) != vhost_hlen) {
>>>
>>> We should copy only sizeof(hdr) instead of vhost_hlen.> > Anything I miss?
>>
>> sizeof(hdr) will be greater than vhost_hlen when neither
>> VIRTIO_NET_F_MRG_RXBUF or VIRTIO_F_VERSION_1 is negotiated.
> 
> Just to make sure we are on the same page I meant we should only
> advance sizeof(struct virtio_net_hdr) here to make sure we can set the
> num_buffers correctly.
> 
> But this is not what the code did here.

This code wrote num_buffers in hdr instead of setting it later.

However, with v10, I changed it again to fill the whole header with zero 
and to set num_buffers later. The end result is identical either way; 
num_buffers has the correct value and the other fields are filled with zero.

Regards,
Akihiko Odaki

> 
> Thanks
> 
>>
>> Regards,
>> Akihiko Odaki
>>
>>>
>>> Thanks
>>>
>>>>
>>>> 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
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>