linux-kernel - [PATCH 3.15 004/122] ibmvscsi: Add memory barriers for send / receive

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Date:	Mon,  7 Jul 2014 16:56:06 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Brian King <brking@...ux.vnet.ibm.com>,
	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@....de>
Subject: [PATCH 3.15 004/122] ibmvscsi: Add memory barriers for send / receive

3.15-stable 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/scsi/ibmvscsi/ibmvscsi.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/scsi/ibmvscsi/ibmvscsi.c
+++ b/drivers/scsi/ibmvscsi/ibmvscsi.c
@@ -185,6 +185,11 @@ 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);
@@ -203,6 +208,11 @@ static int ibmvscsi_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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