> -----Original Message-----
> From: Dipayaan Roy <[email protected]>
> Sent: Tuesday, March 24, 2026 2:14 PM
> To: KY Srinivasan <[email protected]>; Haiyang Zhang
> <[email protected]>; [email protected]; Dexuan Cui
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; [email protected];
> Long Li <[email protected]>; Konstantin Taranov
> <[email protected]>; [email protected];
> [email protected]; [email protected];
> [email protected]; Shiraz Saleem <[email protected]>;
> [email protected]; [email protected]; linux-
> [email protected]; [email protected];
> [email protected]; [email protected]; Dipayaan Roy
> <[email protected]>
> Subject: [PATCH net,v2] net: mana: Fix RX skb truesize accounting
>
> MANA passes rxq->alloc_size to napi_build_skb() for all RX buffers.
> It is correct for fragment-backed RX buffers, where alloc_size matches
> the actual backing allocation used for each packet buffer. However, in
> the non-fragment RX path mana allocates a full page, or a higher-order
> page, per RX buffer. In that case alloc_size only reflects the usable
> packet area and not the actual backing memory.
>
> This causes napi_build_skb() to underestimate the skb backing allocation
> in the single-buffer RX path, so skb->truesize is derived from a value
> smaller than the real RX buffer allocation.
>
> Fix this by updating alloc_size in the non-fragment RX path to the
> actual backing allocation size before it is passed to napi_build_skb().
>
> Fixes: 730ff06d3f5c ("net: mana: Use page pool fragments for RX buffers
> instead of full pages to improve memory efficiency.")
> Signed-off-by: Dipayaan Roy <[email protected]>
Reviewed-by: Haiyang Zhang <[email protected]>
> ---
> Changes in v2:
> - Added maintainers missed in v1.
> ---
> drivers/net/ethernet/microsoft/mana/mana_en.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c
> b/drivers/net/ethernet/microsoft/mana/mana_en.c
> index ea71de39f996..884f8e548174 100644
> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> @@ -766,6 +766,13 @@ static void mana_get_rxbuf_cfg(struct
> mana_port_context *apc,
> }
>
> *frag_count = 1;
> +
> + /* In the single-buffer path, napi_build_skb() must see the
> + * actual backing allocation size so skb->truesize reflects
> + * the full page (or higher-order page), not just the usable
> + * packet area.
> + */
> + *alloc_size = PAGE_SIZE << get_order(*alloc_size);
> return;
> }
>
> --
> 2.43.0
>
