linux-kernel - [PATCH 3.2 13/94] ibmvscsi: Add memory barriers for send / receive

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Message-ID: <lsq.1407170911.994208773@decadent.org.uk>
Date:	Mon, 04 Aug 2014 17:48:31 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Christoph Hellwig" <hch@....de>,
	"Nathan Fontenot" <nfont@...ux.vnet.ibm.com>,
	"Brian King" <brking@...ux.vnet.ibm.com>
Subject: [PATCH 3.2 13/94] ibmvscsi: Add memory barriers for send / receive

3.2.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Brian King <brking@...ux.vnet.ibm.com>

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@...ux.vnet.ibm.com>
Acked-by: Nathan Fontenot <nfont@...ux.vnet.ibm.com>
Signed-off-by: Christoph Hellwig <hch@....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@...adent.org.uk>
---
 drivers/scsi/ibmvscsi/ibmvscsi.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

--- 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
 	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 ibmv
 {
 	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);
 }
 

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