netdev - Re: [RFC PATCH v3 02/12] net: page_pool: create hooks for custom page providers

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Date: Sun, 12 Nov 2023 19:28:52 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Shuah Khan <shuah@...nel.org>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>, 
	Shakeel Butt <shakeelb@...gle.com>, Jeroen de Borst <jeroendb@...gle.com>, 
	Praveen Kaligineedi <pkaligineedi@...gle.com>
Subject: Re: [RFC PATCH v3 02/12] net: page_pool: create hooks for custom page providers

On Fri, Nov 10, 2023 at 3:19 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sun,  5 Nov 2023 18:44:01 -0800 Mina Almasry wrote:
> > diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> > index 6fc5134095ed..d4bea053bb7e 100644
> > --- a/include/net/page_pool/types.h
> > +++ b/include/net/page_pool/types.h
> > @@ -60,6 +60,8 @@ struct page_pool_params {
> >       int             nid;
> >       struct device   *dev;
> >       struct napi_struct *napi;
> > +     u8              memory_provider;
> > +     void            *mp_priv;
> >       enum dma_data_direction dma_dir;
> >       unsigned int    max_len;
> >       unsigned int    offset;
>
> you should rebase on top of net-next
>
> More importantly I was expecting those fields to be gone from params.
> The fact that the page pool is configured to a specific provider
> should be fully transparent to the driver, driver should just tell
> the core what queue its creating the pool from and if there's a dmabuf
> bound for that queue - out pops a pp backed by the dmabuf.
>

My issue with this is that if the driver doesn't support dmabuf then
the driver will accidentally use the pp backed by the dmabuf, allocate
a page from it, then call page_address() on it or something, and
crash.

Currently I avoid that by having the driver be responsible for picking
up the dmabuf from the netdev_rx_queue and giving it to the page pool.
What would be the appropriate way to check for driver support in the
netlink API? Perhaps adding something to ndo_features_check?

-- 
Thanks,
Mina