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Subject[096/244] net/9p: Fix kernel crash with msize 512K
3.0-stable review patch.  If anyone has any objections, please let us know.

------------------
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

commit b49d8b5d7007a673796f3f99688b46931293873e upstream.

With msize equal to 512K (PAGE_SIZE * VIRTQUEUE_NUM), we hit multiple
crashes. This patch fix those.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/9p/trans_virtio.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -263,7 +263,6 @@ p9_virtio_request(struct p9_client *clie
{
int in, out, inp, outp;
struct virtio_chan *chan = client->trans;
- char *rdata = (char *)req->rc+sizeof(struct p9_fcall);
unsigned long flags;
size_t pdata_off = 0;
struct trans_rpage_info *rpinfo = NULL;
@@ -346,7 +345,8 @@ req_retry_pinned:
* Arrange in such a way that server places header in the
* alloced memory and payload onto the user buffer.
*/
- inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
+ inp = pack_sg_list(chan->sg, out,
+ VIRTQUEUE_NUM, req->rc->sdata, 11);
/*
* Running executables in the filesystem may result in
* a read request with kernel buffer as opposed to user buffer.
@@ -366,8 +366,8 @@ req_retry_pinned:
}
in += inp;
} else {
- in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
- req->rc->capacity);
+ in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM,
+ req->rc->sdata, req->rc->capacity);
}

err = virtqueue_add_buf(chan->vq, chan->sg, out, in, req->tc);
@@ -592,7 +592,14 @@ static struct p9_trans_module p9_virtio_
.close = p9_virtio_close,
.request = p9_virtio_request,
.cancel = p9_virtio_cancel,
- .maxsize = PAGE_SIZE*VIRTQUEUE_NUM,
+
+ /*
+ * We leave one entry for input and one entry for response
+ * headers. We also skip one more entry to accomodate, address
+ * that are not at page boundary, that can result in an extra
+ * page in zero copy.
+ */
+ .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
.pref = P9_TRANS_PREF_PAYLOAD_SEP,
.def = 0,
.owner = THIS_MODULE,



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