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

[Jason Wang <jasowang@redhat.com>]

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.

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
> >>>>>
> >>>>
> >>>
> >>
> >
>