net/9p: Fix kernel crash with msize 512K

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>

1 files changed, 12 insertions, 5 deletions

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 175b5135bdc..e317583fcc7 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -263,7 +263,6 @@ p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
 {
         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_trans = {
         .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,