netdev - Re: [PATCH vhost v11 10/10] virtio_net: merge dma operation for one page

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Message-ID: <ZLjul7mYcMujUfxQ@infradead.org>
Date: Thu, 20 Jul 2023 01:21:43 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jason Wang <jasowang@...hat.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	virtualization@...ts.linux-foundation.org,
	"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>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
	bpf@...r.kernel.org
Subject: Re: [PATCH vhost v11 10/10] virtio_net: merge dma operation for one
 page

On Thu, Jul 20, 2023 at 03:41:56PM +0800, Jason Wang wrote:
> > Did you actually check that it works though?
> > Looks like with swiotlb you need to synch to trigger a copy
> > before unmap, and I don't see where it's done in the current
> > patch.
> 
> And this is needed for XDP_REDIRECT as well.

DMA always needs proper syncs, be that for swiotlb or for cache
maintainance, yes.