netdev - [PATCH net 1/2] ibmvnic: Ensure that SCRQ entry reads are correctly ordered

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Message-Id: <1606238776-30259-2-git-send-email-tlfalcon@linux.ibm.com>
Date:   Tue, 24 Nov 2020 11:26:15 -0600
From:   Thomas Falcon <tlfalcon@...ux.ibm.com>
To:     netdev@...r.kernel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, cforno12@...ux.ibm.com,
        ljp@...ux.vnet.ibm.com, ricklind@...ux.ibm.com,
        dnbanerg@...ibm.com, drt@...ux.vnet.ibm.com,
        brking@...ux.vnet.ibm.com, sukadev@...ux.vnet.ibm.com,
        tlfalcon@...ux.ibm.com
Subject: [PATCH net 1/2] ibmvnic: Ensure that SCRQ entry reads are correctly ordered

Ensure that received Subordinate Command-Response Queue (SCRQ)
entries are properly read in order by the driver. These queues
are used in the ibmvnic device to process RX buffer and TX completion
descriptors. dma_rmb barriers have been added after checking for a
pending descriptor to ensure the correct descriptor entry is checked
and after reading the SCRQ descriptor to ensure the entire
descriptor is read before processing.

Fixes: 032c5e828 ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Thomas Falcon <tlfalcon@...ux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 2aa40b2..489ed5e 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2403,6 +2403,8 @@ static int ibmvnic_poll(struct napi_struct *napi, int budget)
 
 		if (!pending_scrq(adapter, adapter->rx_scrq[scrq_num]))
 			break;
+		/* ensure that we do not prematurely exit the polling loop */
+		dma_rmb();
 		next = ibmvnic_next_scrq(adapter, adapter->rx_scrq[scrq_num]);
 		rx_buff =
 		    (struct ibmvnic_rx_buff *)be64_to_cpu(next->
@@ -3098,6 +3100,9 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter *adapter,
 		unsigned int pool = scrq->pool_index;
 		int num_entries = 0;
 
+		/* ensure that the correct descriptor entry is read */
+		dma_rmb();
+
 		next = ibmvnic_next_scrq(adapter, scrq);
 		for (i = 0; i < next->tx_comp.num_comps; i++) {
 			if (next->tx_comp.rcs[i]) {
@@ -3498,6 +3503,9 @@ static union sub_crq *ibmvnic_next_scrq(struct ibmvnic_adapter *adapter,
 	}
 	spin_unlock_irqrestore(&scrq->lock, flags);
 
+	/* ensure that the entire SCRQ descriptor is read */
+	dma_rmb();
+
 	return entry;
 }
 
-- 
1.8.3.1