linux-kernel - Re: [PATCH net-next v2 4/5] page_pool: disable sync for cpu for dmabuf memory provider

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Message-ID: <20241108141812.GL35848@ziepe.ca>
Date: Fri, 8 Nov 2024 10:18:12 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mina Almasry <almasrymina@...gle.com>
Cc: netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	Pavel Begunkov <asml.silence@...il.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Kaiyuan Zhang <kaiyuanz@...gle.com>,
	Samiullah Khawaja <skhawaja@...gle.com>,
	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [PATCH net-next v2 4/5] page_pool: disable sync for cpu for
 dmabuf memory provider

On Thu, Nov 07, 2024 at 09:23:08PM +0000, Mina Almasry wrote:
> dmabuf dma-addresses should not be dma_sync'd for CPU/device. Typically
> its the driver responsibility to dma_sync for CPU, but the driver should
> not dma_sync for CPU if the netmem is actually coming from a dmabuf
> memory provider.

This is not completely true, it is not *all* dmabuf, just the parts of
the dmabuf that are actually MMIO.

If you do this you may want to block accepting dmabufs that have CPU
pages inside them.

Jason