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

[Jason Wang]

On Tue, Mar 11, 2025 at 2:24 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
>
> On 2025/03/11 9:42, Jason Wang wrote:
> > On Mon, Mar 10, 2025 at 3:04 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
> >>
> >> On 2025/03/10 13:43, Jason Wang wrote:
> >>> On Fri, Mar 7, 2025 at 7:02 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> 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@xxxxxxxxxx>
> >>>> Tested-by: Lei Yang <leiyang@xxxxxxxxxx>
> >>>> ---
> >>>>    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?

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
> >>>
> >>
> >
>