[PATCH RFC 1/2] vfio-ccw: forward halt/clear to device if supported

[Cornelia Huck]

The initial version of vfio-ccw did not support forwarding of the
halt or clear functions to the device, and we had to emulate them
instead.

For versions of the vfio-ccw kernel implementation that indeed do
support halt/clear (by indicating them in the fctl of the scsw in
the io_region), we can simply start making use of it. If the kernel
does not support handling halt/clear, fall back to emulation.

Signed-off-by: Cornelia Huck <cohuck@xxxxxxxxxx>
---
 hw/s390x/css.c         | 32 ++++++++++++++++++++++++++++----
 hw/vfio/ccw.c          | 11 +++++++++--
 include/hw/s390x/css.h | 10 +++++++---
 3 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 301bf1772f..b6727d0607 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1180,6 +1180,16 @@ static void sch_handle_start_func_virtual(SubchDev *sch)
 
 }
 
+static IOInstEnding sch_handle_clear_func_passthrough(SubchDev *sch)
+{
+    return s390_ccw_cmd_request(sch);
+}
+
+static IOInstEnding sch_handle_halt_func_passthrough(SubchDev *sch)
+{
+    return s390_ccw_cmd_request(sch);
+}
+
 static IOInstEnding sch_handle_start_func_passthrough(SubchDev *sch)
 {
 
@@ -1233,13 +1243,27 @@ IOInstEnding do_subchannel_work_virtual(SubchDev *sch)
 IOInstEnding do_subchannel_work_passthrough(SubchDev *sch)
 {
     SCSW *s = &sch->curr_status.scsw;
+    static bool no_halt_clear;
 
+    /* if the kernel does not support halt/clear, fall back to emulation */
     if (s->ctrl & SCSW_FCTL_CLEAR_FUNC) {
-        /* TODO: Clear handling */
-        sch_handle_clear_func(sch);
+        if (no_halt_clear) {
+            sch_handle_clear_func(sch);
+        } else {
+            if (sch_handle_clear_func_passthrough(sch) == IOINST_OPNOTSUPP) {
+                no_halt_clear = true;
+                sch_handle_halt_func(sch);
+            }
+        }
     } else if (s->ctrl & SCSW_FCTL_HALT_FUNC) {
-        /* TODO: Halt handling */
-        sch_handle_halt_func(sch);
+        if (no_halt_clear) {
+            sch_handle_halt_func(sch);
+        } else {
+            if (sch_handle_halt_func_passthrough(sch) == IOINST_OPNOTSUPP) {
+                no_halt_clear = true;
+                sch_handle_halt_func(sch);
+            }
+        }
     } else if (s->ctrl & SCSW_FCTL_START_FUNC) {
         return sch_handle_start_func_passthrough(sch);
     }
diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index e67392c5f9..247901ae41 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -60,6 +60,7 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch)
 
     memset(region, 0, sizeof(*region));
 
+    /* orb is only valid for ssch, but does not hurt for other functions */
     memcpy(region->orb_area, &sch->orb, sizeof(ORB));
     memcpy(region->scsw_area, &sch->curr_status.scsw, sizeof(SCSW));
 
@@ -70,8 +71,12 @@ again:
         if (errno == EAGAIN) {
             goto again;
         }
-        error_report("vfio-ccw: wirte I/O region failed with errno=%d", errno);
-        ret = -errno;
+        /* handle not supported operations like halt/clear on older kernels */
+        if (ret != -EOPNOTSUPP) {
+            error_report("vfio-ccw: write I/O region failed with errno=%d",
+                         errno);
+            ret = -errno;
+        }
     } else {
         ret = region->ret_code;
     }
@@ -83,6 +88,8 @@ again:
     case -ENODEV:
     case -EACCES:
         return IOINST_CC_NOT_OPERATIONAL;
+    case -EOPNOTSUPP:
+        return IOINST_OPNOTSUPP;
     case -EFAULT:
     default:
         sch_gen_unit_exception(sch);
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 35facb47d2..e33f26882b 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -100,9 +100,11 @@ typedef struct CcwDataStream {
 } CcwDataStream;
 
 /*
- * IO instructions conclude according to this. Currently we have only
- * cc codes. Valid values are 0, 1, 2, 3 and the generic semantic for
+ * IO instructions conclude according to this. One class of values are
+ * cc codes: Valid values are 0, 1, 2, 3 and the generic semantic for
  * IO instructions is described briefly. For more details consult the PoP.
+ * Additionally, other endings may occur due to internal processing errors
+ * like lack of support for an operation.
  */
 typedef enum IOInstEnding {
     /* produced expected result */
@@ -112,7 +114,9 @@ typedef enum IOInstEnding {
     /* inst. ineffective because busy with previously initiated function */
     IOINST_CC_BUSY = 2,
     /* inst. ineffective because not operational */
-    IOINST_CC_NOT_OPERATIONAL = 3
+    IOINST_CC_NOT_OPERATIONAL = 3,
+    /* internal: operation not supported */
+    IOINST_OPNOTSUPP = 4
 } IOInstEnding;
 
 typedef struct SubchDev SubchDev;
-- 
2.14.3