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

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Message-ID: <Zy41HkR5dDmjVJwl@mini-arch>
Date: Fri, 8 Nov 2024 07:58:22 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Mina Almasry <almasrymina@...gle.com>, 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 11/08, Jason Gunthorpe wrote:
> 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.

We still want udmabufs to work, so probably need some new helper to test
whether a particular netmem is backed by the cpu memory?