Re: [PATCH net-next v7 2/2] page_pool: Track DMA-mapped pages and unmap them when destroying the pool

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Toke Høiland-Jørgensen <toke@redhat.com>
Date: Fri, 04 Apr 2025 12:18:36 +0200

> When enabling DMA mapping in page_pool, pages are kept DMA mapped until
> they are released from the pool, to avoid the overhead of re-mapping the
> pages every time they are used. This causes resource leaks and/or
> crashes when there are pages still outstanding while the device is torn
> down, because page_pool will attempt an unmap through a non-existent DMA
> device on the subsequent page return.

[...]

> -#define PP_MAGIC_MASK ~0x3UL
> +#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
>  
>  /**
>   * struct page_pool_params - page pool parameters
> @@ -173,10 +212,10 @@ struct page_pool {
>  	int cpuid;
>  	u32 pages_state_hold_cnt;
>  
> -	bool has_init_callback:1;	/* slow::init_callback is set */
> +	bool dma_sync;			/* Perform DMA sync for device */

Yunsheng said this change to a full bool is redundant in the v6 thread
¯\_(ツ)_/¯
I hope you've read it.

>  	bool dma_map:1;			/* Perform DMA mapping */
> -	bool dma_sync:1;		/* Perform DMA sync for device */
>  	bool dma_sync_for_cpu:1;	/* Perform DMA sync for cpu */
> +	bool has_init_callback:1;	/* slow::init_callback is set */
>  #ifdef CONFIG_PAGE_POOL_STATS
>  	bool system:1;			/* This is a global percpu pool */
>  #endif

Thanks,
Olek