netdev - [PATCH net 3/3] ibmvnic: Ensure that CRQ entry read/write are correctly ordered

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Date:   Thu, 21 Jan 2021 00:17:10 -0600
From:   Lijun Pan <ljp@...ux.ibm.com>
To:     netdev@...r.kernel.org
Cc:     Lijun Pan <ljp@...ux.ibm.com>
Subject: [PATCH net 3/3] ibmvnic: Ensure that CRQ entry read/write are correctly ordered

Ensure that received Command-Response Queue (CRQ) entries are
properly read/written in order by the driver. dma_rmb barrier
has been added before accessing the CRQ descriptor to ensure
the entire descriptor is read before processing. dma_wmb barrier
is also added to ensure the entire descriptor is written before
future processing.

Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Lijun Pan <ljp@...ux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 933e8fb71a8b..e947eb068163 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -5090,8 +5090,20 @@ static void ibmvnic_tasklet(struct tasklet_struct *t)
 	while (!done) {
 		/* Pull all the valid messages off the CRQ */
 		while ((crq = ibmvnic_next_crq(adapter)) != NULL) {
+			/* Ensure that the entire CRQ descriptor queue->msgs
+			 * has been loaded before reading its contents.
+			 * This barrier makes sure ibmvnic_next_crq()'s
+			 * crq->generic.first & IBMVNIC_CRQ_CMD_RSP is loaded
+			 * before ibmvnic_handle_crq()'s
+			 * switch(gen_crq->first) and switch(gen_crq->cmd).
+			 */
+			dma_rmb();
 			ibmvnic_handle_crq(crq, adapter);
 			crq->generic.first = 0;
+			/* Ensure the entire CRQ descriptor is written before
+			 * future writing.
+			 */
+			dma_wmb();
 		}
 
 		/* remain in tasklet until all
-- 
2.23.0