ibmvscsi: Add memory barriers for send / receive

commit 7114aae02742d6b5c5a0d39a41deb61d415d3717 upstream.

Add a memory barrier prior to sending a new command to the VIOS
to ensure the VIOS does not receive stale data in the command buffer.
Also add a memory barrier when processing the CRQ for completed commands.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Acked-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[bwh: Backported to 3.2: as the iSeries code is still present, these
 functions have different names and live in rpa_vscsi.c.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/scsi/ibmvscsi/rpa_vscsi.c b/drivers/scsi/ibmvscsi/rpa_vscsi.c
index f48ae01..920c02e 100644 (file)
--- a/drivers/scsi/ibmvscsi/rpa_vscsi.c
+++ b/drivers/scsi/ibmvscsi/rpa_vscsi.c
@@ -104,6 +104,11 @@ static struct viosrp_crq *crq_queue_next_crq(struct crq_queue *queue)
        if (crq->valid & 0x80) {
                if (++queue->cur == queue->size)
                        queue->cur = 0;
+
+               /* Ensure the read of the valid bit occurs before reading any
+                * other bits of the CRQ entry
+                */
+               rmb();
        } else
                crq = NULL;
        spin_unlock_irqrestore(&queue->lock, flags);
@@ -122,6 +127,11 @@ static int rpavscsi_send_crq(struct ibmvscsi_host_data *hostdata,
 {
        struct vio_dev *vdev = to_vio_dev(hostdata->dev);
 
+       /*
+        * Ensure the command buffer is flushed to memory before handing it
+        * over to the VIOS to prevent it from fetching any stale data.
+        */
+       mb();
        return plpar_hcall_norets(H_SEND_CRQ, vdev->unit_address, word1, word2);
 }