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Date:   Sun, 30 Apr 2023 21:24:52 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc:     virtualization@lists.linux-foundation.org,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
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        "David S. Miller" <davem@davemloft.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        Christoph Hellwig <hch@infradead.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexander Lobakin <aleksander.lobakin@intel.com>
Subject: Re: [PATCH vhost v7 01/11] virtio_ring: split: separate dma codes
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> +static dma_addr_t vring_sg_address(struct scatterlist *sg)
> +{
> +	if (sg->dma_address)
> +		return sg->dma_address;

0 is a perfectly valid DMA address.  So I have no idea how this is
even supposed to work.