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: <20241115015912.GA559636@ziepe.ca>
Date: Thu, 14 Nov 2024 21:59:12 -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 Fri, Nov 08, 2024 at 11:01:21AM -0800, Mina Almasry wrote:

> > If you do this you may want to block accepting dmabufs that have CPU
> > pages inside them.
> >
> 
> How do I check if the dmabuf has CPU pages inside of it? The only way
> I can think to do that is to sg_page a scatterlist entry, then
> !is_zone_device_page() the page. Or something like that, but I thought
> calling sg_page() on the dmabuf scatterlist was banned now.

I don't know. Many dmabuf scenarios abuse scatter list and the CPU
list is invalid, so you can't reference sg_page().

I think you'd need to discuss with the dmabuf maintainers.

Jason