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

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

[Jon Hunter]

Hi Furong,

On 07/02/2025 08:56, 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@nvidia.com>
> Reported-by: Brad Griffis <bgriffis@nvidia.com>
> Suggested-by: Ido Schimmel <idosch@idosch.org>
> Fixes: df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX path")
> Signed-off-by: Furong Xu <0x1207@gmail.com>
> ---
>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index b34ebb916b89..c0ae7db96f46 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2094,6 +2094,11 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
>   	pp_params.offset = stmmac_rx_offset(priv);
>   	pp_params.max_len = dma_conf->dma_buf_sz;
>   
> +	if (priv->sph) {
> +		pp_params.offset = 0;
> +		pp_params.max_len += stmmac_rx_offset(priv);
> +	}
> +
>   	rx_q->page_pool = page_pool_create(&pp_params);
>   	if (IS_ERR(rx_q->page_pool)) {
>   		ret = PTR_ERR(rx_q->page_pool);


Thanks for sending this. I can confirm that it fixes the issue we are 
seeing and so ...

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Cheers
Jon

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nvpublic

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

[Thierry Reding]

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On Fri, Feb 07, 2025 at 01:41:49PM +0000, Jon Hunter wrote:
> Hi Furong,
> 
> On 07/02/2025 08:56, 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@nvidia.com>
> > Reported-by: Brad Griffis <bgriffis@nvidia.com>
> > Suggested-by: Ido Schimmel <idosch@idosch.org>
> > Fixes: df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX path")
> > Signed-off-by: Furong Xu <0x1207@gmail.com>
> > ---
> >   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index b34ebb916b89..c0ae7db96f46 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -2094,6 +2094,11 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
> >   	pp_params.offset = stmmac_rx_offset(priv);
> >   	pp_params.max_len = dma_conf->dma_buf_sz;
> > +	if (priv->sph) {
> > +		pp_params.offset = 0;
> > +		pp_params.max_len += stmmac_rx_offset(priv);
> > +	}
> > +
> >   	rx_q->page_pool = page_pool_create(&pp_params);
> >   	if (IS_ERR(rx_q->page_pool)) {
> >   		ret = PTR_ERR(rx_q->page_pool);
> 
> 
> Thanks for sending this. I can confirm that it fixes the issue we are seeing
> and so ...
> 
> Tested-by: Jon Hunter <jonathanh@nvidia.com>

Yes, I can confirm as well. I've tested based on the discussion in the
earlier thread and had the equivalent of this patch (modulo the ->sph
check, but that's always true on this system), so:

Tested-by: Thierry Reding <treding@nvidia.com>

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