python/qemu: accel: Strengthen kvm_available() checks

Currently kvm_available() checks for the presence of kvm module
and, if target and host arches don't mismatch. This patch adds
an 3rd checking: if QEMU binary was compiled with kvm
support.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20191216191438.93418-4-wainersm@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>

python/qemu/accel.py

@@ -46,9 +46,24 @@ def list_accel(qemu_bin):
     # Skip the first line which is the header.
     return [acc.strip() for acc in out.splitlines()[1:]]
 
-def kvm_available(target_arch=None):
-    host_arch = os.uname()[4]
-    if target_arch and target_arch != host_arch:
-        if target_arch != ADDITIONAL_ARCHES.get(host_arch):
-            return False
-    return os.access("/dev/kvm", os.R_OK | os.W_OK)
+def kvm_available(target_arch=None, qemu_bin=None):
+    """
+    Check if KVM is available using the following heuristic:
+      - Kernel module is present in the host;
+      - Target and host arches don't mismatch;
+      - KVM is enabled in the QEMU binary.
+
+    @param target_arch (str): target architecture
+    @param qemu_bin (str): path to the QEMU binary
+    @return True if kvm is available, otherwise False.
+    """
+    if not os.access("/dev/kvm", os.R_OK | os.W_OK):
+        return False
+    if target_arch:
+        host_arch = os.uname()[4]
+        if target_arch != host_arch:
+            if target_arch != ADDITIONAL_ARCHES.get(host_arch):
+                return False
+    if qemu_bin and "kvm" not in list_accel(qemu_bin):
+        return False
+    return True