netdev - Re: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message

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Date:   Mon, 28 Dec 2020 17:12:44 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, sgarzare@...hat.com,
        Parav Pandit <parav@...dia.com>, akpm@...ux-foundation.org,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        axboe@...nel.dk, bcrl@...ck.org, corbet@....net,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message

On Mon, Dec 28, 2020 at 4:43 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2020/12/28 下午4:14, Yongji Xie wrote:
> >> I see. So all the above two questions are because VHOST_IOTLB_INVALIDATE
> >> is expected to be synchronous. This need to be solved by tweaking the
> >> current VDUSE API or we can re-visit to go with descriptors relaying first.
> >>
> > Actually all vdpa related operations are synchronous in current
> > implementation. The ops.set_map/dma_map/dma_unmap should not return
> > until the VDUSE_UPDATE_IOTLB/VDUSE_INVALIDATE_IOTLB message is replied
> > by userspace. Could it solve this problem?
>
>
>   I was thinking whether or not we need to generate IOTLB_INVALIDATE
> message to VDUSE during dma_unmap (vduse_dev_unmap_page).
>
> If we don't, we're probably fine.
>

It seems not feasible. This message will be also used in the
virtio-vdpa case to notify userspace to unmap some pages during
consistent dma unmapping. Maybe we can document it to make sure the
users can handle the message correctly.

Thanks,
Yongji