[PATCH 4.19 02/17] ibmvnic: Ensure that CRQ entry read are correctly ordered

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Lijun Pan <ljp@linux.ibm.com>

commit e41aec79e62fa50f940cf222d1e9577f14e149dc upstream.

Ensure that received Command-Response Queue (CRQ) entries are
properly read 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.

Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
Link: https://lore.kernel.org/r/20210128013442.88319-1-ljp@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/ibm/ibmvnic.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -4434,6 +4434,12 @@ static void ibmvnic_tasklet(void *data)
 	while (!done) {
 		/* Pull all the valid messages off the CRQ */
 		while ((crq = ibmvnic_next_crq(adapter)) != NULL) {
+			/* 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;
 		}