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

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Message-ID: <CACGkMEu9tynRgTh__3p_vSqOekSirbVgS90rd5dUiJru9oV1eg@mail.gmail.com>
Date: Tue, 11 Mar 2025 08:42:13 +0800
From: Jason Wang <jasowang@...hat.com>
To: Akihiko Odaki <akihiko.odaki@...nix.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 Mon, Mar 10, 2025 at 3:04 PM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>
> 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.

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.

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
> >
>