netdev - Re: [PATCH net-next v1] xsk: introduce xsk_dma

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Date:   Sun, 23 Apr 2023 16:42:07 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Jason Wang <jasowang@...hat.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH net-next v1] xsk: introduce xsk_dma_cbs

On Sun, Apr 23, 2023 at 08:45:20AM +0200, Greg KH wrote:
> On Sun, Apr 23, 2023 at 02:25:45PM +0800, Xuan Zhuo wrote:
> > The purpose of this patch is to allow driver pass the own dma callbacks
> > to xsk.
> > 
> > This is to cope with the scene of virtio-net. If virtio does not have
> > VIRTIO_F_ACCESS_PLATFORM, then virtio cannot use DMA API. In this case,
> > xsk cannot use DMA API directly to achieve DMA address. Based on this
> > scene, we must let xsk support driver to use the driver's dma callbacks.
> 
> Why does virtio need to use dma?  That seems to go against the overall
> goal of virtio's new security restrictions that are being proposed
> (where they do NOT want it to use dma as it is not secure).

Yes, they exactly use dma, specifically dma into bounce buffer.