netdev - Re: [PATCH vhost v6 09/10] virtio_net: set premapped mode by find

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Message-ID: <1711935607.4691076-1-xuanzhuo@linux.alibaba.com>
Date: Mon, 1 Apr 2024 09:40:07 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux.dev,
 "Michael S. Tsirkin" <mst@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH vhost v6 09/10] virtio_net: set premapped mode by find_vqs()

On Fri, 29 Mar 2024 11:20:08 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Thu, Mar 28, 2024 at 4:27 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > On Thu, 28 Mar 2024 16:05:02 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > On Wed, Mar 27, 2024 at 7:14 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > > >
> > > > Now, the virtio core can set the premapped mode by find_vqs().
> > > > If the premapped can be enabled, the dma array will not be
> > > > allocated. So virtio-net use the api of find_vqs to enable the
> > > > premapped.
> > > >
> > > > Judge the premapped mode by the vq->premapped instead of saving
> > > > local variable.
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > > ---
> > >
> > > I wonder what's the reason to keep a fallback when premapped is not enabled?
> >
> > Rethink this.
> >
> > I think you are right. We can remove the fallback.
> >
> > Because we have the virtio dma apis that wrap all the cases.
> > So I will remove the fallback from the virtio-net in next version.
>
> Ok.
>
> >
> > But we still need to export the premapped to the drivers.
> > Because we can enable the AF_XDP only when premapped is true.
>
> I may miss something but it should work like
>
> enable AF_XDP -> enable remapping
>
> So can we fail during remapping enablement?

YES.

Enabling the premapped mode may fail, then we must stop to enable AF_XDP.

AF-XDP requires that we export the dma dev to the af-xdp.
We can do that only when the virtio core works with use_dma_api.
Other other side, if we support the page-pool in future, we may have the
same requirement.

Thanks.

>
> THanks
>
> >
> > Thanks
> >
> >
> > >
> > > Thanks
> > >
> >
>