vfio: ccw: validate the count field of a ccw before pinning

If the count field of a ccw is zero, there is no need to
try to pin page(s) for it. Let's check the count value
before starting pinning operations.

Reviewed-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Message-Id: <20171011023822.42948-3-bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 722f8b8..d8f98ad 100644 (file)
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -105,7 +105,10 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
 {
        int ret = 0;
 
-       if (!len || pa->pa_nr)
+       if (!len)
+               return 0;
+
+       if (pa->pa_nr)
                return -EINVAL;
 
        pa->pa_iova = iova;
@@ -501,6 +504,16 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
 
        ccw = chain->ch_ccw + idx;
 
+       if (!ccw->count) {
+               /*
+                * We just want the translation result of any direct ccw
+                * to be an IDA ccw, so let's add the IDA flag for it.
+                * Although the flag will be ignored by firmware.
+                */
+               ccw->flags |= CCW_FLAG_IDA;
+               return 0;
+       }
+
        /*
         * Pin data page(s) in memory.
         * The number of pages actually is the count of the idaws which will be
@@ -541,6 +554,9 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
 
        ccw = chain->ch_ccw + idx;
 
+       if (!ccw->count)
+               return 0;
+
        /* Calculate size of idaws. */
        ret = copy_from_iova(cp->mdev, &idaw_iova, ccw->cda, sizeof(idaw_iova));
        if (ret)