[libvirt] [PATCH 3/4] qemu: Fix probing of AMD SEV support

[Erik Skultety]

So the procedure to detect SEV support works like this:
1) we detect that sev-guest is among the QOM types and set the cap flag
2) we probe the monitor for SEV support
    - this is tricky, because QEMU with compiled SEV support will always
    report -object sev-guest and query-sev-capabilities command, that
    however doesn't mean SEV is supported
3) depending on what the monitor returned, we either keep or clear the
capability flag for SEV

Commit a349c6c21c6 added an explicit check for "GenericError" in the
monitor reply to prevent libvirtd to spam logs about missing
'query-sev-capabilities' command. At the same time though, it returned
success in this case which means that we didn't clear the capability
flag afterwards and happily formatted SEV into qemuCaps.

Signed-off-by: Erik Skultety <eskultet at redhat.com>
---
 src/qemu/qemu_monitor_json.c                     | 9 +++++----
 tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml | 1 -
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 3f99f39120..b0963ed887 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -6459,11 +6459,12 @@ qemuMonitorJSONGetSEVCapabilities(qemuMonitorPtr mon,
         goto cleanup;
 
     /* Both -object sev-guest and query-sev-capabilities can be present
-     * even if SEV is not available */
-    if (qemuMonitorJSONHasError(reply, "GenericError")) {
-        ret = 0;
+     * even if SEV is not available. We have to check for "GenericError" first,
+     * in order not to spam libvirtd logs.
+     * NOTE: We return failure here too so that the capability gets cleared
+     * later */
+    if (qemuMonitorJSONHasError(reply, "GenericError"))
         goto cleanup;
-    }
 
     if (qemuMonitorJSONCheckError(cmd, reply) < 0)
         goto cleanup;
diff --git a/tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml
index efddcbc6a5..2b47337449 100644
--- a/tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml
+++ b/tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml
@@ -211,7 +211,6 @@
   <flag name='tpm-emulator'/>
   <flag name='mch'/>
   <flag name='mch.extended-tseg-mbytes'/>
-  <flag name='sev-guest'/>
   <flag name='usb-storage.werror'/>
   <flag name='egl-headless'/>
   <flag name='vfio-pci.display'/>
-- 
2.14.4