Message-Id: <20250728053546.4829-1-byungchul@sk.com>
Date: Mon, 28 Jul 2025 14:35:46 +0900
From: Byungchul Park <byungchul@...com>
To: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: kernel_team@...ynix.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	almasrymina@...gle.com,
	hawk@...nel.org,
	toke@...hat.com,
	asml.silence@...il.com
Subject: [RFC net-next] netmem: replace __netmem_clear_lsb() with netmem_to_nmdesc()

> Now that we have struct netmem_desc, it'd better access the pp fields
> via struct netmem_desc rather than struct net_iov.
> 
> Introduce netmem_to_nmdesc() for safely converting netmem_ref to
> netmem_desc regardless of the type underneath e.i. netmem_desc, net_iov.
> 
> While at it, remove __netmem_clear_lsb() and make netmem_to_nmdesc()
> used instead.

+cc kernel_team@...ynix.com

	Byungchul

> Signed-off-by: Byungchul Park <byungchul@...com>
> ---
>  include/net/netmem.h   | 33 ++++++++++++++++-----------------
>  net/core/netmem_priv.h | 16 ++++++++--------
>  2 files changed, 24 insertions(+), 25 deletions(-)
> 
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index f7dacc9e75fd..33ae444a9745 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -265,24 +265,23 @@ static inline struct netmem_desc *__netmem_to_nmdesc(netmem_ref netmem)
>  	return (__force struct netmem_desc *)netmem;
>  }
>  
> -/* __netmem_clear_lsb - convert netmem_ref to struct net_iov * for access to
> - * common fields.
> - * @netmem: netmem reference to extract as net_iov.
> +/* netmem_to_nmdesc - convert netmem_ref to struct netmem_desc * for
> + * access to common fields.
> + * @netmem: netmem reference to get netmem_desc.
>   *
> - * All the sub types of netmem_ref (page, net_iov) have the same pp, pp_magic,
> - * dma_addr, and pp_ref_count fields at the same offsets. Thus, we can access
> - * these fields without a type check to make sure that the underlying mem is
> - * net_iov or page.
> + * All the sub types of netmem_ref (netmem_desc, net_iov) have the same
> + * pp, pp_magic, dma_addr, and pp_ref_count fields via netmem_desc.
>   *
> - * The resulting value of this function can only be used to access the fields
> - * that are NET_IOV_ASSERT_OFFSET'd. Accessing any other fields will result in
> - * undefined behavior.
> - *
> - * Return: the netmem_ref cast to net_iov* regardless of its underlying type.
> + * Return: the pointer to struct netmem_desc * regardless of its
> + * underlying type.
>   */
> -static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
> +static inline struct netmem_desc *netmem_to_nmdesc(netmem_ref netmem)
>  {
> -	return (struct net_iov *)((__force unsigned long)netmem & ~NET_IOV);
> +	if (netmem_is_net_iov(netmem))
> +		return &((struct net_iov *)((__force unsigned long)netmem &
> +					    ~NET_IOV))->desc;
> +
> +	return __netmem_to_nmdesc(netmem);
>  }
>  
>  /* XXX: How to extract netmem_desc from page must be changed, once
> @@ -320,12 +319,12 @@ static inline struct page_pool *__netmem_get_pp(netmem_ref netmem)
>  
>  static inline struct page_pool *netmem_get_pp(netmem_ref netmem)
>  {
> -	return __netmem_clear_lsb(netmem)->pp;
> +	return netmem_to_nmdesc(netmem)->pp;
>  }
>  
>  static inline atomic_long_t *netmem_get_pp_ref_count_ref(netmem_ref netmem)
>  {
> -	return &__netmem_clear_lsb(netmem)->pp_ref_count;
> +	return &netmem_to_nmdesc(netmem)->pp_ref_count;
>  }
>  
>  static inline bool netmem_is_pref_nid(netmem_ref netmem, int pref_nid)
> @@ -390,7 +389,7 @@ static inline bool netmem_is_pfmemalloc(netmem_ref netmem)
>  
>  static inline unsigned long netmem_get_dma_addr(netmem_ref netmem)
>  {
> -	return __netmem_clear_lsb(netmem)->dma_addr;
> +	return netmem_to_nmdesc(netmem)->dma_addr;
>  }
>  
>  void get_netmem(netmem_ref netmem);
> diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
> index cd95394399b4..23175cb2bd86 100644
> --- a/net/core/netmem_priv.h
> +++ b/net/core/netmem_priv.h
> @@ -5,19 +5,19 @@
>  
>  static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
>  {
> -	return __netmem_clear_lsb(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
> +	return netmem_to_nmdesc(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
>  }
>  
>  static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
>  {
> -	__netmem_clear_lsb(netmem)->pp_magic |= pp_magic;
> +	netmem_to_nmdesc(netmem)->pp_magic |= pp_magic;
>  }
>  
>  static inline void netmem_clear_pp_magic(netmem_ref netmem)
>  {
> -	WARN_ON_ONCE(__netmem_clear_lsb(netmem)->pp_magic & PP_DMA_INDEX_MASK);
> +	WARN_ON_ONCE(netmem_to_nmdesc(netmem)->pp_magic & PP_DMA_INDEX_MASK);
>  
> -	__netmem_clear_lsb(netmem)->pp_magic = 0;
> +	netmem_to_nmdesc(netmem)->pp_magic = 0;
>  }
>  
>  static inline bool netmem_is_pp(netmem_ref netmem)
> @@ -27,13 +27,13 @@ static inline bool netmem_is_pp(netmem_ref netmem)
>  
>  static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
>  {
> -	__netmem_clear_lsb(netmem)->pp = pool;
> +	netmem_to_nmdesc(netmem)->pp = pool;
>  }
>  
>  static inline void netmem_set_dma_addr(netmem_ref netmem,
>  				       unsigned long dma_addr)
>  {
> -	__netmem_clear_lsb(netmem)->dma_addr = dma_addr;
> +	netmem_to_nmdesc(netmem)->dma_addr = dma_addr;
>  }
>  
>  static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
> @@ -43,7 +43,7 @@ static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
>  	if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
>  		return 0;
>  
> -	magic = __netmem_clear_lsb(netmem)->pp_magic;
> +	magic = netmem_to_nmdesc(netmem)->pp_magic;
>  
>  	return (magic & PP_DMA_INDEX_MASK) >> PP_DMA_INDEX_SHIFT;
>  }
> @@ -57,6 +57,6 @@ static inline void netmem_set_dma_index(netmem_ref netmem,
>  		return;
>  
>  	magic = netmem_get_pp_magic(netmem) | (id << PP_DMA_INDEX_SHIFT);
> -	__netmem_clear_lsb(netmem)->pp_magic = magic;
> +	netmem_to_nmdesc(netmem)->pp_magic = magic;
>  }
>  #endif
> 
> base-commit: fa582ca7e187a15e772e6a72fe035f649b387a60
> -- 
> 2.17.1
> 

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