linux-kernel - Re: [PATCH net-next v2 3/5] page_pool: Set `dma_sync` to false for devmem memory provider

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Message-ID: <c0b6d0a3-66d4-49aa-87fe-85a4346d723b@gmail.com>
Date: Fri, 8 Nov 2024 16:34:44 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn <willemb@...gle.com>,
 Kaiyuan Zhang <kaiyuanz@...gle.com>, Samiullah Khawaja
 <skhawaja@...gle.com>, linux-kernel@...r.kernel.org
Cc: "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>,
 Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH net-next v2 3/5] page_pool: Set `dma_sync` to false for
 devmem memory provider

On 11/7/24 21:23, Mina Almasry wrote:
> From: Samiullah Khawaja <skhawaja@...gle.com>
> 
> Move the `dma_map` and `dma_sync` checks to `page_pool_init` to make
> them generic. Set dma_sync to false for devmem memory provider because
> the dma_sync APIs should not be used for dma_buf backed devmem memory
> provider.
> 
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> 
> ---
>   net/core/devmem.c    | 9 ++++-----
>   net/core/page_pool.c | 3 +++
>   2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index 11b91c12ee11..826d0b00159f 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -331,11 +331,10 @@ int mp_dmabuf_devmem_init(struct page_pool *pool)
>   	if (!binding)
>   		return -EINVAL;
>   
> -	if (!pool->dma_map)
> -		return -EOPNOTSUPP;
> -
> -	if (pool->dma_sync)
> -		return -EOPNOTSUPP;
> +	/* dma-buf dma addresses should not be used with
> +	 * dma_sync_for_cpu/device. Force disable dma_sync.
> +	 */
> +	pool->dma_sync = false;
>   
>   	if (pool->p.order != 0)
>   		return -E2BIG;
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 77de79c1933b..528dd4d18eab 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -287,6 +287,9 @@ static int page_pool_init(struct page_pool *pool,
>   	}
>   
>   	if (pool->mp_priv) {
> +		if (!pool->dma_map || !pool->dma_sync)

Is there a reason why ->dma_sync is enforced for all providers?
It sounds like a devmem fix, on the other hand I don't really
care as we don't have drivers yet implementing queue api / etc.
but not passing PP_FLAG_DMA_SYNC_DEV.

Also, putting fixes first in the series or sending them separately
reduces backporting headache.

-- 
Pavel Begunkov