linux-kernel - [PATCH net-next 05/16] idpf: fix Rx descriptor ready check barrier in splitq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250305162132.1106080-6-aleksander.lobakin@intel.com>
Date: Wed,  5 Mar 2025 17:21:21 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: intel-wired-lan@...ts.osuosl.org
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>,
	Michal Kubiak <michal.kubiak@...el.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	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>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Simon Horman <horms@...nel.org>,
	bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next 05/16] idpf: fix Rx descriptor ready check barrier in splitq

No idea what the current barrier position was meant for. At that point,
nothing is read from the descriptor, only the pointer to the actual one
is fetched.
The correct barrier usage here is after the generation check, so that
only the first qword is read if the descriptor is not yet ready and we
need to stop polling. Debatable on coherent DMA as the Rx descriptor
size is <= cacheline size, but anyway, the current barrier position
only makes the codegen worse.

Fixes: 3a8845af66ed ("idpf: add RX splitq napi poll support")
Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
---
 drivers/net/ethernet/intel/idpf/idpf_txrx.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
index 6254806c2072..c15833928ea1 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
@@ -3232,18 +3232,14 @@ static int idpf_rx_splitq_clean(struct idpf_rx_queue *rxq, int budget)
 		/* get the Rx desc from Rx queue based on 'next_to_clean' */
 		rx_desc = &rxq->rx[ntc].flex_adv_nic_3_wb;
 
-		/* This memory barrier is needed to keep us from reading
-		 * any other fields out of the rx_desc
-		 */
-		dma_rmb();
-
 		/* if the descriptor isn't done, no work yet to do */
 		gen_id = le16_get_bits(rx_desc->pktlen_gen_bufq_id,
 				       VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M);
-
 		if (idpf_queue_has(GEN_CHK, rxq) != gen_id)
 			break;
 
+		dma_rmb();
+
 		rxdid = FIELD_GET(VIRTCHNL2_RX_FLEX_DESC_ADV_RXDID_M,
 				  rx_desc->rxdid_ucast);
 		if (rxdid != VIRTCHNL2_RXDID_2_FLEX_SPLITQ) {
-- 
2.48.1