netdev - Re: [PATCH net v1] net: stmmac: Apply new page pool parameters when SPH is enabled

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Message-ID: <Z6miASgDGKfGH9qO@shredder>
Date: Mon, 10 Feb 2025 08:51:45 +0200
From: Ido Schimmel <idosch@...sch.org>
To: Furong Xu <0x1207@...il.com>
Cc: netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>, xfr@...look.com,
	Jon Hunter <jonathanh@...dia.com>,
	Brad Griffis <bgriffis@...dia.com>
Subject: Re: [PATCH net v1] net: stmmac: Apply new page pool parameters when
 SPH is enabled

On Fri, Feb 07, 2025 at 04:56:39PM +0800, Furong Xu wrote:
> Commit df542f669307 ("net: stmmac: Switch to zero-copy in
> non-XDP RX path") makes DMA write received frame into buffer at offset
> of NET_SKB_PAD and sets page pool parameters to sync from offset of
> NET_SKB_PAD. But when Header Payload Split is enabled, the header is
> written at offset of NET_SKB_PAD, while the payload is written at
> offset of zero. Uncorrect offset parameter for the payload breaks dma
> coherence [1] since both CPU and DMA touch the page buffer from offset
> of zero which is not handled by the page pool sync parameter.
> 
> And in case the DMA cannot split the received frame, for example,
> a large L2 frame, pp_params.max_len should grow to match the tail
> of entire frame.
> 
> [1] https://lore.kernel.org/netdev/d465f277-bac7-439f-be1d-9a47dfe2d951@nvidia.com/
> 
> Reported-by: Jon Hunter <jonathanh@...dia.com>
> Reported-by: Brad Griffis <bgriffis@...dia.com>
> Suggested-by: Ido Schimmel <idosch@...sch.org>
> Fixes: df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX path")
> Signed-off-by: Furong Xu <0x1207@...il.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>