s390x/event-facility: variable-length event masks

The architecture supports masks of variable length for sclp write
event mask. We currently only support 4 byte event masks, as that
is what Linux uses.

Let's extend this to the maximum mask length supported by the
architecture and return 0 to the guest for the mask bits we don't
support in core.

Initial patch by: Cornelia Huck <cornelia.huck@de.ibm.com>

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Message-Id: <1507729193-9747-1-git-send-email-jjherne@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

2 files changed, 45 insertions, 10 deletions

diff --git a/hw/s390x/event-facility.c b/hw/s390x/event-facility.c
index 34b2faf013..b0f71f4554 100644
--- a/hw/s390x/event-facility.c
+++ b/hw/s390x/event-facility.c
@@ -259,23 +259,46 @@ out:
     return;
 }
 
+/* copy up to dst_len bytes and fill the rest of dst with zeroes */
+static void copy_mask(uint8_t *dst, uint8_t *src, uint16_t dst_len,
+                      uint16_t src_len)
+{
+    int i;
+
+    for (i = 0; i < dst_len; i++) {
+        dst[i] = i < src_len ? src[i] : 0;
+    }
+}
+
 static void write_event_mask(SCLPEventFacility *ef, SCCB *sccb)
 {
     WriteEventMask *we_mask = (WriteEventMask *) sccb;
+    uint16_t mask_length = be16_to_cpu(we_mask->mask_length);
+    uint32_t tmp_mask;
 
-    /* Attention: We assume that Linux uses 4-byte masks, what it actually
-       does. Architecture allows for masks of variable size, though */
-    if (be16_to_cpu(we_mask->mask_length) != 4) {
+    if (!mask_length || (mask_length > SCLP_EVENT_MASK_LEN_MAX)) {
         sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_MASK_LENGTH);
         goto out;
     }
 
+    /*
+     * Note: We currently only support masks up to 4 byte length;
+     *       the remainder is filled up with zeroes. Linux uses
+     *       a 4 byte mask length.
+     */
+
     /* keep track of the guest's capability masks */
-    ef->receive_mask = be32_to_cpu(we_mask->cp_receive_mask);
+    copy_mask((uint8_t *)&tmp_mask, WEM_CP_RECEIVE_MASK(we_mask, mask_length),
+              sizeof(tmp_mask), mask_length);
+    ef->receive_mask = be32_to_cpu(tmp_mask);
 
     /* return the SCLP's capability masks to the guest */
-    we_mask->send_mask = cpu_to_be32(get_host_send_mask(ef));
-    we_mask->receive_mask = cpu_to_be32(get_host_receive_mask(ef));
+    tmp_mask = cpu_to_be32(get_host_send_mask(ef));
+    copy_mask(WEM_RECEIVE_MASK(we_mask, mask_length), (uint8_t *)&tmp_mask,
+              mask_length, sizeof(tmp_mask));
+    tmp_mask = cpu_to_be32(get_host_receive_mask(ef));
+    copy_mask(WEM_SEND_MASK(we_mask, mask_length), (uint8_t *)&tmp_mask,
+              mask_length, sizeof(tmp_mask));
 
     sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_COMPLETION);
 
diff --git a/include/hw/s390x/event-facility.h b/include/hw/s390x/event-facility.h
index def1bb0c03..5119b9b7f0 100644
--- a/include/hw/s390x/event-facility.h
+++ b/include/hw/s390x/event-facility.h
@@ -49,16 +49,28 @@
 #define TYPE_SCLP_CPU_HOTPLUG "sclp-cpu-hotplug"
 #define TYPE_SCLP_QUIESCE "sclpquiesce"
 
+#define SCLP_EVENT_MASK_LEN_MAX 1021
+
 typedef struct WriteEventMask {
     SCCBHeader h;
     uint16_t _reserved;
     uint16_t mask_length;
-    uint32_t cp_receive_mask;
-    uint32_t cp_send_mask;
-    uint32_t receive_mask;
-    uint32_t send_mask;
+    uint8_t masks[];
+/*
+ * Layout of the masks is
+ *  uint8_t cp_receive_mask[mask_length];
+ *  uint8_t cp_send_mask[mask_length];
+ *  uint8_t receive_mask[mask_length];
+ *  uint8_t send_mask[mask_length];
+ * where 1 <= mask_length <= SCLP_EVENT_MASK_LEN_MAX
+ */
 } QEMU_PACKED WriteEventMask;
 
+#define WEM_CP_RECEIVE_MASK(wem, mask_len) ((wem)->masks)
+#define WEM_CP_SEND_MASK(wem, mask_len) ((wem)->masks + (mask_len))
+#define WEM_RECEIVE_MASK(wem, mask_len) ((wem)->masks + 2 * (mask_len))
+#define WEM_SEND_MASK(wem, mask_len) ((wem)->masks + 3 * (mask_len))
+
 typedef struct EventBufferHeader {
     uint16_t length;
     uint8_t  type;