vm_event: Add a new opcode to get VM_EVENT_INTERFACE_VERSION

Currently, the VM_EVENT_INTERFACE_VERSION is determined at runtime, by
inspecting the corresponding field in a vm_event_request. This helper
opcode will query the hypervisor supported version before the vm_event
related structures and layout are set-up.

Signed-off-by: Petre Pircalabu <ppircalabu@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>

tools/libxc/include/xenctrl.h

@@ -2003,6 +2003,11 @@ int xc_set_mem_access_multi(xc_interface *xch, uint32_t domain_id,
 int xc_get_mem_access(xc_interface *xch, uint32_t domain_id,
                       uint64_t pfn, xenmem_access_t *access);
 
+/*
+ * Returns the VM_EVENT_INTERFACE version.
+ */
+int xc_vm_event_get_version(xc_interface *xch);
+
 /***
  * Monitor control operations.
  *

tools/libxc/xc_vm_event.c

@@ -35,7 +35,7 @@ int xc_vm_event_control(xc_interface *xch, uint32_t domain_id, unsigned int op,
 
     rc = do_domctl(xch, &domctl);
     if ( !rc && port )
-        *port = domctl.u.vm_event_op.port;
+        *port = domctl.u.vm_event_op.u.enable.port;
     return rc;
 }
 
@@ -156,6 +156,22 @@ void *xc_vm_event_enable(xc_interface *xch, uint32_t domain_id, int param,
     return ring_page;
 }
 
+int xc_vm_event_get_version(xc_interface *xch)
+{
+    DECLARE_DOMCTL;
+    int rc;
+
+    domctl.cmd = XEN_DOMCTL_vm_event_op;
+    domctl.domain = DOMID_INVALID;
+    domctl.u.vm_event_op.op = XEN_VM_EVENT_GET_VERSION;
+    domctl.u.vm_event_op.mode = XEN_DOMCTL_VM_EVENT_OP_MONITOR;
+
+    rc = do_domctl(xch, &domctl);
+    if ( !rc )
+        rc = domctl.u.vm_event_op.u.version;
+    return rc;
+}
+
 /*
  * Local variables:
  * mode: C

xen/common/domctl.c

@@ -392,6 +392,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
     switch ( op->cmd )
     {
     case XEN_DOMCTL_test_assign_device:
+    case XEN_DOMCTL_vm_event_op:
         if ( op->domain == DOMID_INVALID )
         {
     case XEN_DOMCTL_createdomain:

xen/common/vm_event.c

@@ -88,7 +88,7 @@ static int vm_event_enable(
     if ( rc < 0 )
         goto err;
 
-    (*ved)->xen_port = vec->port = rc;
+    (*ved)->xen_port = vec->u.enable.port = rc;
 
     /* Prepare ring buffer */
     FRONT_RING_INIT(&(*ved)->front_ring,
@@ -592,6 +592,15 @@ int vm_event_domctl(struct domain *d, struct xen_domctl_vm_event_op *vec,
 {
     int rc;
 
+    if ( vec->op == XEN_VM_EVENT_GET_VERSION )
+    {
+        vec->u.version = VM_EVENT_INTERFACE_VERSION;
+        return 0;
+    }
+
+    if ( unlikely(d == NULL) )
+        return -ESRCH;
+
     rc = xsm_vm_event_control(XSM_PRIV, d, vec->mode, vec->op);
     if ( rc )
         return rc;

xen/include/public/domctl.h

@@ -781,6 +781,7 @@ struct xen_domctl_gdbsx_domstatus {
 #define XEN_VM_EVENT_ENABLE               0
 #define XEN_VM_EVENT_DISABLE              1
 #define XEN_VM_EVENT_RESUME               2
+#define XEN_VM_EVENT_GET_VERSION          3
 
 /*
  * Domain memory paging
@@ -843,7 +844,13 @@ struct xen_domctl_vm_event_op {
     uint32_t       op;           /* XEN_VM_EVENT_* */
     uint32_t       mode;         /* XEN_DOMCTL_VM_EVENT_OP_* */
 
-    uint32_t port;              /* OUT: event channel for ring */
+    union {
+        struct {
+            uint32_t port;       /* OUT: event channel for ring */
+        } enable;
+
+        uint32_t version;
+    } u;
 };
 
 /*