target/i386/monitor: Return QMP error when SEV is not enabled for guest

If the management layer tries to inject a secret, it gets an empty
response in case the guest doesn't have SEV enabled, or the binary
is built without SEV:

  { "execute": "sev-inject-launch-secret",
    "arguments": { "packet-header": "mypkt", "secret": "mypass", "gpa": 4294959104 }
  }
  {
      "return": {
      }
  }

Make it clearer by returning an error:

  { "execute": "sev-inject-launch-secret",
    "arguments": { "packet-header": "mypkt", "secret": "mypass", "gpa": 4294959104 }
  }
  {
      "error": {
          "class": "GenericError",
          "desc": "SEV not enabled for guest"
      }
  }

Note: we will remove the sev_inject_launch_secret() stub in few commits,
      so we don't bother to add error_setg() there.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211007161716.453984-7-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/target/i386/monitor.c b/target/i386/monitor.c
index eabbeb9..ea83667 100644
--- a/target/i386/monitor.c
+++ b/target/i386/monitor.c
@@ -28,6 +28,7 @@
 #include "monitor/hmp-target.h"
 #include "monitor/hmp.h"
 #include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qerror.h"
 #include "sysemu/kvm.h"
 #include "sysemu/sev.h"
 #include "qapi/error.h"
@@ -743,6 +744,10 @@ void qmp_sev_inject_launch_secret(const char *packet_hdr,
                                   bool has_gpa, uint64_t gpa,
                                   Error **errp)
 {
+    if (!sev_enabled()) {
+        error_setg(errp, "SEV not enabled for guest");
+        return;
+    }
     if (!has_gpa) {
         uint8_t *data;
         struct sev_secret_area *area;