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authorJared Rossi <jrossi@linux.ibm.com>2020-05-06 17:24:40 -0400
committerCornelia Huck <cohuck@redhat.com>2020-06-02 13:14:08 +0200
commit725b94d74128cd208bfdd446ad6b5f4b38cf5395 (patch)
tree394d06fb3b404e9dc4e293fedaa4c18bc186049a
parente1750a3d9abbea2ece29cac8dc5a6f5bc19c1492 (diff)
vfio-ccw: Enable transparent CCW IPL from DASD
Remove the explicit prefetch check when using vfio-ccw devices. This check does not trigger in practice as all Linux channel programs are intended to use prefetch. It is expected that all ORBs issued by Linux will request prefetch. Although non-prefetching ORBs are not rejected, they will prefetch nonetheless. A warning is issued up to once per 5 seconds when a forced prefetch occurs. A non-prefetch ORB does not necessarily result in an error, however frequent encounters with non-prefetch ORBs indicate that channel programs are being executed in a way that is inconsistent with what the guest is requesting. While there is currently no known case of an error caused by forced prefetch, it is possible in theory that forced prefetch could result in an error if applied to a channel program that is dependent on non-prefetch. Signed-off-by: Jared Rossi <jrossi@linux.ibm.com> Reviewed-by: Eric Farman <farman@linux.ibm.com> Message-Id: <20200506212440.31323-2-jrossi@linux.ibm.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
-rw-r--r--Documentation/s390/vfio-ccw.rst6
-rw-r--r--drivers/s390/cio/vfio_ccw_cp.c19
2 files changed, 18 insertions, 7 deletions
diff --git a/Documentation/s390/vfio-ccw.rst b/Documentation/s390/vfio-ccw.rst
index fca9c4f5bd9c..23e7d136f8b4 100644
--- a/Documentation/s390/vfio-ccw.rst
+++ b/Documentation/s390/vfio-ccw.rst
@@ -335,6 +335,12 @@ device.
The current code allows the guest to start channel programs via
START SUBCHANNEL, and to issue HALT SUBCHANNEL and CLEAR SUBCHANNEL.
+Currently all channel programs are prefetched, regardless of the
+p-bit setting in the ORB. As a result, self modifying channel
+programs are not supported. For this reason, IPL has to be handled as
+a special case by a userspace/guest program; this has been implemented
+in QEMU's s390-ccw bios as of QEMU 4.1.
+
vfio-ccw supports classic (command mode) channel I/O only. Transport
mode (HPF) is not supported.
diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 3645d1720c4b..b9febc581b1f 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -8,6 +8,7 @@
* Xiao Feng Ren <renxiaof@linux.vnet.ibm.com>
*/
+#include <linux/ratelimit.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/iommu.h>
@@ -625,23 +626,27 @@ static int ccwchain_fetch_one(struct ccwchain *chain,
* the target channel program from @orb->cmd.iova to the new ccwchain(s).
*
* Limitations:
- * 1. Supports only prefetch enabled mode.
- * 2. Supports idal(c64) ccw chaining.
- * 3. Supports 4k idaw.
+ * 1. Supports idal(c64) ccw chaining.
+ * 2. Supports 4k idaw.
*
* Returns:
* %0 on success and a negative error value on failure.
*/
int cp_init(struct channel_program *cp, struct device *mdev, union orb *orb)
{
+ /* custom ratelimit used to avoid flood during guest IPL */
+ static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 1);
int ret;
/*
- * XXX:
- * Only support prefetch enable mode now.
+ * We only support prefetching the channel program. We assume all channel
+ * programs executed by supported guests likewise support prefetching.
+ * Executing a channel program that does not specify prefetching will
+ * typically not cause an error, but a warning is issued to help identify
+ * the problem if something does break.
*/
- if (!orb->cmd.pfch)
- return -EOPNOTSUPP;
+ if (!orb->cmd.pfch && __ratelimit(&ratelimit_state))
+ dev_warn(mdev, "Prefetching channel program even though prefetch not specified in ORB");
INIT_LIST_HEAD(&cp->ccwchain_list);
memcpy(&cp->orb, orb, sizeof(*orb));