Re: [PATCH net-next v12 01/10] virtio_net: Add functions for hashing

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

On 2025/06/04 10:18, Jason Wang wrote:
> On Tue, Jun 3, 2025 at 1:31 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
>> On 2025/06/03 12:19, Jason Wang wrote:
>>> On Fri, May 30, 2025 at 12:50 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>>>
>>>> They are useful to implement VIRTIO_NET_F_RSS and
>>>> VIRTIO_NET_F_HASH_REPORT.
>>>>
>>>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>>>> Tested-by: Lei Yang <leiyang@redhat.com>
>>>> ---
>>>>    include/linux/virtio_net.h | 188 +++++++++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 188 insertions(+)
>>>>
>>>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>>>> index 02a9f4dc594d..426f33b4b824 100644
>>>> --- a/include/linux/virtio_net.h
>>>> +++ b/include/linux/virtio_net.h
>>>> @@ -9,6 +9,194 @@
>>>>    #include <uapi/linux/tcp.h>
>>>>    #include <uapi/linux/virtio_net.h>
>>>>
>>>> +struct virtio_net_hash {
>>>> +       u32 value;
>>>> +       u16 report;
>>>> +};
>>>> +
>>>> +struct virtio_net_toeplitz_state {
>>>> +       u32 hash;
>>>> +       const u32 *key;
>>>> +};
>>>> +
>>>> +#define VIRTIO_NET_SUPPORTED_HASH_TYPES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 | \
>>>> +                                        VIRTIO_NET_RSS_HASH_TYPE_TCPv4 | \
>>>> +                                        VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | \
>>>> +                                        VIRTIO_NET_RSS_HASH_TYPE_IPv6 | \
>>>> +                                        VIRTIO_NET_RSS_HASH_TYPE_TCPv6 | \
>>>> +                                        VIRTIO_NET_RSS_HASH_TYPE_UDPv6)
>>>> +
>>>> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
>>>> +
>>>> +static inline void virtio_net_toeplitz_convert_key(u32 *input, size_t len)
>>>> +{
>>>> +       while (len >= sizeof(*input)) {
>>>> +               *input = be32_to_cpu((__force __be32)*input);
>>>> +               input++;
>>>> +               len -= sizeof(*input);
>>>> +       }
>>>> +}
>>>> +
>>>> +static inline void virtio_net_toeplitz_calc(struct virtio_net_toeplitz_state *state,
>>>> +                                           const __be32 *input, size_t len)
>>>> +{
>>>> +       while (len >= sizeof(*input)) {
>>>> +               for (u32 map = be32_to_cpu(*input); map; map &= (map - 1)) {
>>>> +                       u32 i = ffs(map);
>>>> +
>>>> +                       state->hash ^= state->key[0] << (32 - i) |
>>>> +                                      (u32)((u64)state->key[1] >> i);
>>>> +               }
>>>> +
>>>> +               state->key++;
>>>> +               input++;
>>>> +               len -= sizeof(*input);
>>>> +       }
>>>> +}
>>>> +
>>>> +static inline u8 virtio_net_hash_key_length(u32 types)
>>>> +{
>>>> +       size_t len = 0;
>>>> +
>>>> +       if (types & VIRTIO_NET_HASH_REPORT_IPv4)
>>>> +               len = max(len,
>>>> +                         sizeof(struct flow_dissector_key_ipv4_addrs));
>>>> +
>>>> +       if (types &
>>>> +           (VIRTIO_NET_HASH_REPORT_TCPv4 | VIRTIO_NET_HASH_REPORT_UDPv4))
>>>> +               len = max(len,
>>>> +                         sizeof(struct flow_dissector_key_ipv4_addrs) +
>>>> +                         sizeof(struct flow_dissector_key_ports));
>>>> +
>>>> +       if (types & VIRTIO_NET_HASH_REPORT_IPv6)
>>>> +               len = max(len,
>>>> +                         sizeof(struct flow_dissector_key_ipv6_addrs));
>>>> +
>>>> +       if (types &
>>>> +           (VIRTIO_NET_HASH_REPORT_TCPv6 | VIRTIO_NET_HASH_REPORT_UDPv6))
>>>> +               len = max(len,
>>>> +                         sizeof(struct flow_dissector_key_ipv6_addrs) +
>>>> +                         sizeof(struct flow_dissector_key_ports));
>>>> +
>>>> +       return len + sizeof(u32);
>>>> +}
>>>> +
>>>> +static inline u32 virtio_net_hash_report(u32 types,
>>>> +                                        const struct flow_keys_basic *keys)
>>>> +{
>>>> +       switch (keys->basic.n_proto) {
>>>> +       case cpu_to_be16(ETH_P_IP):
>>>> +               if (!(keys->control.flags & FLOW_DIS_IS_FRAGMENT)) {
>>>> +                       if (keys->basic.ip_proto == IPPROTO_TCP &&
>>>> +                           (types & VIRTIO_NET_RSS_HASH_TYPE_TCPv4))
>>>> +                               return VIRTIO_NET_HASH_REPORT_TCPv4;
>>>> +
>>>> +                       if (keys->basic.ip_proto == IPPROTO_UDP &&
>>>> +                           (types & VIRTIO_NET_RSS_HASH_TYPE_UDPv4))
>>>> +                               return VIRTIO_NET_HASH_REPORT_UDPv4;
>>>> +               }
>>>> +
>>>> +               if (types & VIRTIO_NET_RSS_HASH_TYPE_IPv4)
>>>> +                       return VIRTIO_NET_HASH_REPORT_IPv4;
>>>> +
>>>> +               return VIRTIO_NET_HASH_REPORT_NONE;
>>>> +
>>>> +       case cpu_to_be16(ETH_P_IPV6):
>>>> +               if (!(keys->control.flags & FLOW_DIS_IS_FRAGMENT)) {
>>>> +                       if (keys->basic.ip_proto == IPPROTO_TCP &&
>>>> +                           (types & VIRTIO_NET_RSS_HASH_TYPE_TCPv6))
>>>> +                               return VIRTIO_NET_HASH_REPORT_TCPv6;
>>>> +
>>>> +                       if (keys->basic.ip_proto == IPPROTO_UDP &&
>>>> +                           (types & VIRTIO_NET_RSS_HASH_TYPE_UDPv6))
>>>> +                               return VIRTIO_NET_HASH_REPORT_UDPv6;
>>>> +               }
>>>> +
>>>> +               if (types & VIRTIO_NET_RSS_HASH_TYPE_IPv6)
>>>> +                       return VIRTIO_NET_HASH_REPORT_IPv6;
>>>> +
>>>> +               return VIRTIO_NET_HASH_REPORT_NONE;
>>>> +
>>>> +       default:
>>>> +               return VIRTIO_NET_HASH_REPORT_NONE;
>>>> +       }
>>>> +}
>>>> +
>>>> +static inline void virtio_net_hash_rss(const struct sk_buff *skb,
>>>> +                                      u32 types, const u32 *key,
>>>> +                                      struct virtio_net_hash *hash)
>>>> +{
>>>> +       struct virtio_net_toeplitz_state toeplitz_state = { .key = key };
>>>> +       struct flow_keys flow;
>>>> +       struct flow_keys_basic flow_basic;
>>>> +       u16 report;
>>>> +
>>>> +       if (!skb_flow_dissect_flow_keys(skb, &flow, 0)) {
>>>> +               hash->report = VIRTIO_NET_HASH_REPORT_NONE;
>>>> +               return;
>>>> +       }
>>>> +
>>>> +       flow_basic = (struct flow_keys_basic) {
>>>> +               .control = flow.control,
>>>> +               .basic = flow.basic
>>>> +       };
>>>> +
>>>> +       report = virtio_net_hash_report(types, &flow_basic);
>>>> +
>>>> +       switch (report) {
>>>> +       case VIRTIO_NET_HASH_REPORT_IPv4:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v4addrs,
>>>> +                                        sizeof(flow.addrs.v4addrs));
>>>> +               break;
>>>> +
>>>> +       case VIRTIO_NET_HASH_REPORT_TCPv4:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v4addrs,
>>>> +                                        sizeof(flow.addrs.v4addrs));
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state, &flow.ports.ports,
>>>> +                                        sizeof(flow.ports.ports));
>>>> +               break;
>>>> +
>>>> +       case VIRTIO_NET_HASH_REPORT_UDPv4:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v4addrs,
>>>> +                                        sizeof(flow.addrs.v4addrs));
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state, &flow.ports.ports,
>>>> +                                        sizeof(flow.ports.ports));
>>>> +               break;
>>>> +
>>>> +       case VIRTIO_NET_HASH_REPORT_IPv6:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v6addrs,
>>>> +                                        sizeof(flow.addrs.v6addrs));
>>>> +               break;
>>>> +
>>>> +       case VIRTIO_NET_HASH_REPORT_TCPv6:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v6addrs,
>>>> +                                        sizeof(flow.addrs.v6addrs));
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state, &flow.ports.ports,
>>>> +                                        sizeof(flow.ports.ports));
>>>> +               break;
>>>> +
>>>> +       case VIRTIO_NET_HASH_REPORT_UDPv6:
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state,
>>>> +                                        (__be32 *)&flow.addrs.v6addrs,
>>>> +                                        sizeof(flow.addrs.v6addrs));
>>>> +               virtio_net_toeplitz_calc(&toeplitz_state, &flow.ports.ports,
>>>> +                                        sizeof(flow.ports.ports));
>>>> +               break;
>>>> +
>>>> +       default:
>>>> +               hash->report = VIRTIO_NET_HASH_REPORT_NONE;
>>>> +               return;
>>>
>>> So I still think we need a comment here to explain why this is not an
>>> issue if the device can report HASH_XXX_EX. Or we need to add the
>>> support, since this is the code from the driver side, I don't think we
>>> need to worry about the device implementation issues.
>>
>> This is on the device side, and don't report HASH_TYPE_XXX_EX.
>>
>>>
>>> For the issue of the number of options, does the spec forbid fallback
>>> to VIRTIO_NET_HASH_REPORT_NONE? If not, we can do that.
>>
>> 5.1.6.4.3.4 "IPv6 packets with extension header" says:
>>   > If VIRTIO_NET_HASH_TYPE_TCP_EX is set and the packet has a TCPv6
>>   > header, the hash is calculated over the following fields:
>>   > - Home address from the home address option in the IPv6 destination
>>   >   options header. If the extension header is not present, use the
>>   >   Source IPv6 address.
>>   > - IPv6 address that is contained in the Routing-Header-Type-2 from the
>>   >   associated extension header. If the extension header is not present,
>>   >   use the Destination IPv6 address.
>>   > - Source TCP port
>>   > - Destination TCP port
>>
>> Therefore, if VIRTIO_NET_HASH_TYPE_TCP_EX is set, the packet has a TCPv6
>> and an home address option in the IPv6 destination options header is
>> present, the hash is calculated over the home address. If the hash is
>> not calculated over the home address in such a case, the device is
>> contradicting with this section and violating the spec. The same goes
>> for the other HASH_TYPE_XXX_EX types and Routing-Header-Type-2.
> 
> Just to make sure we are one the same page. I meant:
> 
> 1) If the hash is not calculated over the home address (in the case of
> IPv6 destination destination), it can still report
> VIRTIO_NET_RSS_HASH_TYPE_IPv6. This is what you implemented in your
> series. So the device can simply fallback to e.g TCPv6 if it can't
> understand all or part of the IPv6 options.

The spec says it can fallback if "the extension header is not present", 
not if the device can't understand the extension header.

> 2) the VIRTIO_NET_SUPPORTED_HASH_TYPES is not checked against the
> tun_vnet_ioctl_sethash(), so userspace may set
> VIRTIO_NET_HASH_TYPE_TCP_EX regardless of what has been returned by
> tun_vnet_ioctl_gethashtypes(). In this case they won't get
> VIRTIO_NET_HASH_TYPE_TCP_EX.

That's right. It's the responsibility of the userspace to set only the 
supported hash types.

> 3) implementing part of the hash types might complicate the migration
> or at least we need to describe the expectations of libvirt or other
> management in this case. For example, do we plan to have a dedicated
> Qemu command line like:
> 
> -device virtio-net-pci,hash_report=on,supported_hash_types=X,Y,Z?

I posted a patch series to implement such a command line for vDPA[1]. 
The patch series that wires this tuntap feature up[2] reuses the 
infrastructure so it doesn't bring additional complexity.

[1] 
https://lore.kernel.org/qemu-devel/20250530-vdpa-v1-0-5af4109b1c19@daynix.com/
[2] 
https://lore.kernel.org/qemu-devel/20250530-hash-v5-0-343d7d7a8200@daynix.com/

Regards,
Akihiko Odaki