Re: [PULL 08/83] vdpa: Restore hash calculation state

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 19, 2023 at 09:32:28AM -0700, Stefan Hajnoczi wrote:
> On Wed, 18 Oct 2023 at 08:56, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > From: Hawkins Jiawei <yin31149@gmail.com>
> >
> > This patch introduces vhost_vdpa_net_load_rss() to restore
> > the hash calculation state at device's startup.
> >
> > Note that vhost_vdpa_net_load_rss() has `do_rss` argument,
> > which allows future code to reuse this function to restore
> > the receive-side scaling state when the VIRTIO_NET_F_RSS
> > feature is enabled in SVQ. Currently, vhost_vdpa_net_load_rss()
> > could only be invoked when `do_rss` is set to false.
> >
> > Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
> > Message-Id: <f5ffad10699001107022851e0560cb394039d6b0.1693297766.git.yin31149@gmail.com>
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  net/vhost-vdpa.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 91 insertions(+)
> >
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 4b7c3b81b8..40d0bcbc0b 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -817,6 +817,88 @@ static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n,
> >      return 0;
> >  }
> >
> > +static int vhost_vdpa_net_load_rss(VhostVDPAState *s, const VirtIONet *n,
> > +                                   struct iovec *out_cursor,
> > +                                   struct iovec *in_cursor, bool do_rss)
> > +{
> > +    struct virtio_net_rss_config cfg;
> > +    ssize_t r;
> > +    g_autofree uint16_t *table = NULL;
> > +
> > +    /*
> > +     * According to VirtIO standard, "Initially the device has all hash
> > +     * types disabled and reports only VIRTIO_NET_HASH_REPORT_NONE.".
> > +     *
> > +     * Therefore, there is no need to send this CVQ command if the
> > +     * driver disable the all hash types, which aligns with
> > +     * the device's defaults.
> > +     *
> > +     * Note that the device's defaults can mismatch the driver's
> > +     * configuration only at live migration.
> > +     */
> > +    if (!n->rss_data.enabled ||
> > +        n->rss_data.hash_types == VIRTIO_NET_HASH_REPORT_NONE) {
> > +        return 0;
> > +    }
> > +
> > +    cfg.hash_types = cpu_to_le32(n->rss_data.hash_types);
> > +
> > +    /*
> > +     * According to VirtIO standard, "Field reserved MUST contain zeroes.
> > +     * It is defined to make the structure to match the layout of
> > +     * virtio_net_rss_config structure, defined in 5.1.6.5.7.".
> > +     *
> > +     * Therefore, we need to zero the fields in struct virtio_net_rss_config,
> > +     * which corresponds the `reserved` field in
> > +     * struct virtio_net_hash_config.
> > +     */
> > +    memset(&cfg.indirection_table_mask, 0,
> > +           sizeof_field(struct virtio_net_hash_config, reserved));
> 
> Please take a look at the following CI failure:
> 
> In file included from /usr/include/string.h:495,
> from /home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/include/qemu/osdep.h:116,
> from ../net/vhost-vdpa.c:12:
> In function ‘memset’,
> inlined from ‘vhost_vdpa_net_load_rss’ at ../net/vhost-vdpa.c:874:9:
> /usr/include/s390x-linux-gnu/bits/string_fortified.h:71:10: error:
> ‘__builtin_memset’ offset [7, 12] from the object at ‘cfg’ is out of
> the bounds of referenced subobject ‘indirection_table_mask’ with type
> ‘short unsigned int’ at offset 4 [-Werror=array-bounds]
> 71 | return __builtin___memset_chk (__dest, __ch, __len, __bos0 (__dest));
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> https://gitlab.com/qemu-project/qemu/-/jobs/5329820077

Hmm yes - the trick it's trying to implement is this:


struct virtio_net_rss_config {
        uint32_t hash_types;
        uint16_t indirection_table_mask;
        uint16_t unclassified_queue;
        uint16_t indirection_table[1/* + indirection_table_mask */];
        uint16_t max_tx_vq;
        uint8_t hash_key_length;
        uint8_t hash_key_data[/* hash_key_length */];
};


...

struct virtio_net_hash_config {
        uint32_t hash_types;
        /* for compatibility with virtio_net_rss_config */
        uint16_t reserved[4];
        uint8_t hash_key_length;
        uint8_t hash_key_data[/* hash_key_length */];
};


as you see layout matches.



Using a union is probably the right way to address this.


Dropped for now, thanks!



> > +
> > +    table = g_malloc_n(n->rss_data.indirections_len,
> > +                       sizeof(n->rss_data.indirections_table[0]));
> > +    for (int i = 0; i < n->rss_data.indirections_len; ++i) {
> > +        table[i] = cpu_to_le16(n->rss_data.indirections_table[i]);
> > +    }
> > +
> > +    /*
> > +     * Consider that virtio_net_handle_rss() currently does not restore the
> > +     * hash key length parsed from the CVQ command sent from the guest into
> > +     * n->rss_data and uses the maximum key length in other code, so we also
> > +     * employthe the maxium key length here.
> > +     */
> > +    cfg.hash_key_length = sizeof(n->rss_data.key);
> > +
> > +    const struct iovec data[] = {
> > +        {
> > +            .iov_base = &cfg,
> > +            .iov_len = offsetof(struct virtio_net_rss_config,
> > +                                indirection_table),
> > +        }, {
> > +            .iov_base = table,
> > +            .iov_len = n->rss_data.indirections_len *
> > +                       sizeof(n->rss_data.indirections_table[0]),
> > +        }, {
> > +            .iov_base = &cfg.max_tx_vq,
> > +            .iov_len = offsetof(struct virtio_net_rss_config, hash_key_data) -
> > +                       offsetof(struct virtio_net_rss_config, max_tx_vq),
> > +        }, {
> > +            .iov_base = (void *)n->rss_data.key,
> > +            .iov_len = sizeof(n->rss_data.key),
> > +        }
> > +    };
> > +
> > +    r = vhost_vdpa_net_load_cmd(s, out_cursor, in_cursor,
> > +                                VIRTIO_NET_CTRL_MQ,
> > +                                VIRTIO_NET_CTRL_MQ_HASH_CONFIG,
> > +                                data, ARRAY_SIZE(data));
> > +    if (unlikely(r < 0)) {
> > +        return r;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> >  static int vhost_vdpa_net_load_mq(VhostVDPAState *s,
> >                                    const VirtIONet *n,
> >                                    struct iovec *out_cursor,
> > @@ -842,6 +924,15 @@ static int vhost_vdpa_net_load_mq(VhostVDPAState *s,
> >          return r;
> >      }
> >
> > +    if (!virtio_vdev_has_feature(&n->parent_obj, VIRTIO_NET_F_HASH_REPORT)) {
> > +        return 0;
> > +    }
> > +
> > +    r = vhost_vdpa_net_load_rss(s, n, out_cursor, in_cursor, false);
> > +    if (unlikely(r < 0)) {
> > +        return r;
> > +    }
> > +
> >      return 0;
> >  }
> >
> > --
> > MST
> >
> >