net: mana: Fix RX skb truesize accounting

[ Upstream commit f73896b4197ed53cf0894657c899265ef7c86b7a ]

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 <dipayanroy@linux.microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Link: https://patch.msgid.link/acLUhLpLum6qrD/N@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 50d4437a518f..8e72cb6ccbc1 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -660,6 +660,13 @@ 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;
 	}