vfio-ccw: Move guest_cp storage into common struct

Rather than allocating/freeing a piece of memory every time
we try to figure out how long a CCW chain is, let's use a piece
of memory allocated for each device.

The io_mutex added with commit 4f76617378ee9 ("vfio-ccw: protect
the I/O region") is held for the duration of the VFIO_CCW_EVENT_IO_REQ
event that accesses/uses this space, so there should be no race
concerns with another CPU attempting an (unexpected) SSCH for the
same device.

Suggested-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Message-Id: <20190618202352.39702-2-farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

1 files changed, 4 insertions, 19 deletions

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 90d86e1354c1..f358502376be 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -16,12 +16,6 @@
 
 #include "vfio_ccw_cp.h"
 
-/*
- * Max length for ccw chain.
- * XXX: Limit to 256, need to check more?
- */
-#define CCWCHAIN_LEN_MAX	256
-
 struct pfn_array {
 	/* Starting guest physical I/O address. */
 	unsigned long		pa_iova;
@@ -386,7 +380,7 @@ static void ccwchain_cda_free(struct ccwchain *chain, int idx)
  */
 static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
 {
-	struct ccw1 *ccw, *p;
+	struct ccw1 *ccw = cp->guest_cp;
 	int cnt;
 
 	/*
@@ -394,15 +388,9 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
 	 * Currently the chain length is limited to CCWCHAIN_LEN_MAX (256).
 	 * So copying 2K is enough (safe).
 	 */
-	p = ccw = kcalloc(CCWCHAIN_LEN_MAX, sizeof(*ccw), GFP_KERNEL);
-	if (!ccw)
-		return -ENOMEM;
-
 	cnt = copy_ccw_from_iova(cp, ccw, iova, CCWCHAIN_LEN_MAX);
-	if (cnt) {
-		kfree(ccw);
+	if (cnt)
 		return cnt;
-	}
 
 	cnt = 0;
 	do {
@@ -413,10 +401,8 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
 		 * orb specified one of the unsupported formats, we defer
 		 * checking for IDAWs in unsupported formats to here.
 		 */
-		if ((!cp->orb.cmd.c64 || cp->orb.cmd.i2k) && ccw_is_idal(ccw)) {
-			kfree(p);
+		if ((!cp->orb.cmd.c64 || cp->orb.cmd.i2k) && ccw_is_idal(ccw))
 			return -EOPNOTSUPP;
-		}
 
 		/*
 		 * We want to keep counting if the current CCW has the
@@ -435,7 +421,6 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
 	if (cnt == CCWCHAIN_LEN_MAX + 1)
 		cnt = -EINVAL;
 
-	kfree(p);
 	return cnt;
 }
 
@@ -461,7 +446,7 @@ static int ccwchain_handle_ccw(u32 cda, struct channel_program *cp)
 	struct ccwchain *chain;
 	int len, ret;
 
-	/* Get chain length. */
+	/* Copy the chain from cda to cp, and count the CCWs in it */
 	len = ccwchain_calc_length(cda, cp);
 	if (len < 0)
 		return len;