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From:   Vincent Whitchurch <vincent.whitchurch@axis.com>
To:     gregkh@linuxfoundation.org, arnd@arndb.de
Cc:     sudeep.dutt@intel.com, ashutosh.dixit@intel.com,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, tiwei.bie@intel.com,
        luto@kernel.org, Vincent Whitchurch <rabinv@axis.com>
Subject: [PATCH] mic: vop: Fix broken virtqueues
Date:   Tue, 29 Jan 2019 11:22:07 +0100
Message-Id: <20190129102207.9577-1-vincent.whitchurch@axis.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

VOP is broken in mainline since commit 1ce9e6055fa0a9043 ("virtio_ring:
introduce packed ring support"); attempting to use the virtqueues leads
to various kernel crashes.  I'm testing it with my not-yet-merged
loopback patches, but even the in-tree MIC hardware cannot work.

The problem is not in the referenced commit per se, but is due to the
following hack in vop_find_vq() which depends on the layout of private
structures in other source files, which that commit happened to change:

  /*
   * To reassign the used ring here we are directly accessing
   * struct vring_virtqueue which is a private data structure
   * in virtio_ring.c. At the minimum, a BUILD_BUG_ON() in
   * vring_new_virtqueue() would ensure that
   *  (&vq->vring == (struct vring *) (&vq->vq + 1));
   */
  vr = (struct vring *)(vq + 1);
  vr->used = used;

Fix vop by using __vring_new_virtqueue() to create the needed vring
layout from the start, instead of attempting to patch in the used ring
later.  __vring_new_virtqueue() was added way back in commit
2a2d1382fe9dcc ("virtio: Add improved queue allocation API") in order to
address mic's usecase, according to the commit message.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
 drivers/misc/mic/vop/vop_main.c | 60 +++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 26 deletions(-)

diff --git a/drivers/misc/mic/vop/vop_main.c b/drivers/misc/mic/vop/vop_main.c
index d2b9782eee87..fef45bf6d519 100644
--- a/drivers/misc/mic/vop/vop_main.c
+++ b/drivers/misc/mic/vop/vop_main.c
@@ -284,6 +284,26 @@ static void vop_del_vqs(struct virtio_device *dev)
 		vop_del_vq(vq, idx++);
 }
 
+static struct virtqueue *vop_new_virtqueue(unsigned int index,
+				      unsigned int num,
+				      struct virtio_device *vdev,
+				      bool context,
+				      void *pages,
+				      bool (*notify)(struct virtqueue *vq),
+				      void (*callback)(struct virtqueue *vq),
+				      const char *name,
+				      void *used)
+{
+	bool weak_barriers = false;
+	struct vring vring;
+
+	vring_init(&vring, num, pages, MIC_VIRTIO_RING_ALIGN);
+	vring.used = used;
+
+	return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
+				     notify, callback, name);
+}
+
 /*
  * This routine will assign vring's allocated in host/io memory. Code in
  * virtio_ring.c however continues to access this io memory as if it were local
@@ -303,7 +323,6 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
 	struct _mic_vring_info __iomem *info;
 	void *used;
 	int vr_size, _vr_size, err, magic;
-	struct vring *vr;
 	u8 type = ioread8(&vdev->desc->type);
 
 	if (index >= ioread8(&vdev->desc->num_vq))
@@ -322,17 +341,7 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
 		return ERR_PTR(-ENOMEM);
 	vdev->vr[index] = va;
 	memset_io(va, 0x0, _vr_size);
-	vq = vring_new_virtqueue(
-				index,
-				le16_to_cpu(config.num), MIC_VIRTIO_RING_ALIGN,
-				dev,
-				false,
-				ctx,
-				(void __force *)va, vop_notify, callback, name);
-	if (!vq) {
-		err = -ENOMEM;
-		goto unmap;
-	}
+
 	info = va + _vr_size;
 	magic = ioread32(&info->magic);
 
@@ -341,7 +350,6 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
 		goto unmap;
 	}
 
-	/* Allocate and reassign used ring now */
 	vdev->used_size[index] = PAGE_ALIGN(sizeof(__u16) * 3 +
 					     sizeof(struct vring_used_elem) *
 					     le16_to_cpu(config.num));
@@ -351,8 +359,17 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
 		err = -ENOMEM;
 		dev_err(_vop_dev(vdev), "%s %d err %d\n",
 			__func__, __LINE__, err);
-		goto del_vq;
+		goto unmap;
+	}
+
+	vq = vop_new_virtqueue(index, le16_to_cpu(config.num), dev, ctx,
+			       (void __force *)va, vop_notify, callback,
+			       name, used);
+	if (!vq) {
+		err = -ENOMEM;
+		goto free_used;
 	}
+
 	vdev->used[index] = dma_map_single(&vpdev->dev, used,
 					    vdev->used_size[index],
 					    DMA_BIDIRECTIONAL);
@@ -360,26 +377,17 @@ static struct virtqueue *vop_find_vq(struct virtio_device *dev,
 		err = -ENOMEM;
 		dev_err(_vop_dev(vdev), "%s %d err %d\n",
 			__func__, __LINE__, err);
-		goto free_used;
+		goto del_vq;
 	}
 	writeq(vdev->used[index], &vqconfig->used_address);
-	/*
-	 * To reassign the used ring here we are directly accessing
-	 * struct vring_virtqueue which is a private data structure
-	 * in virtio_ring.c. At the minimum, a BUILD_BUG_ON() in
-	 * vring_new_virtqueue() would ensure that
-	 *  (&vq->vring == (struct vring *) (&vq->vq + 1));
-	 */
-	vr = (struct vring *)(vq + 1);
-	vr->used = used;
 
 	vq->priv = vdev;
 	return vq;
+del_vq:
+	vring_del_virtqueue(vq);
 free_used:
 	free_pages((unsigned long)used,
 		   get_order(vdev->used_size[index]));
-del_vq:
-	vring_del_virtqueue(vq);
 unmap:
 	vpdev->hw_ops->unmap(vpdev, vdev->vr[index]);
 	return ERR_PTR(err);
-- 
2.20.0