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

Pierre Morel <pmorel@xxxxxxxxxxxxx> · Wed, 16 May 2018 15:53:48 +0200

On 15/05/2018 18:01, Cornelia Huck wrote:
On Fri, 11 May 2018 11:53:52 +0200
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

On 09/05/2018 17:49, Cornelia Huck wrote:
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;

Couldn't we introduce ABI versioning ?
Can you elaborate what you're referring to?

If you mean checking capabilities of the kernel or so: If we can avoid
that and just try (and stop if it does not work), I'd prefer that (no
dependencies).

VFIO_CHECK_EXTENSION is already used in different drivers
for this kind of interface extension.
We could use it to setup appropriate callbacks for scsh/csch/xsch/hsch
depending on the extension argument.


The IOINST_OPNOTSUPP is a bit ugly, but I did not see a more elegant
way to pass 'not supported' up to the caller.


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany







