linux-kernel - Re: [PATCH v3 7/7] eni_vdpa: add vDPA driver for Alibaba ENI

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Date:   Mon, 27 Sep 2021 06:36:34 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        wei.yang1@...ux.alibaba.com
Subject: Re: [PATCH v3 7/7] eni_vdpa: add vDPA driver for Alibaba ENI

On Sun, Sep 26, 2021 at 12:18:26PM +0800, Jason Wang wrote:
> > > I wonder if the following can work with ENI:
> > >
> > > -device virtio-net-pci,mrg_rxbuf=off
> > >
> > > ?
> >
> > ENI didn't work.
> > I will remove F_MRG_RXBUF when get_features.
> 
> I think we need to fail FEATURE_OK if F_MRG_RXBUF is not negotiated.
> Since VERSION_1 requires a fixed header length even if F_MRG_RXBUF is
> not negotiated.
> 
> But this trick doesn't come for free. If some driver doesn't support
> mrg_rxbuf, it won't work.
> 
> Thanks

Yea. Ugh. Down the road I think we'll add legacy support to vdpa on
strongly ordered systems.  Doing it in userspace is just too messy imho.
But yes, this kind of hack is probably ok for weakly ordered systems.
BTW we need to set VIRTIO_F_ORDER_PLATFORM, right?

-- 
MST