feat(balloon): allow balloon device with secret_free

Now that discard_range() uses fallocate(PUNCH_HOLE) for MAP_SHARED
guest_memfd regions, the balloon can properly reclaim memory when
secret_free is enabled. Remove the restriction that prevented
combining balloon with secret_free.

Signed-off-by: Jack Thomson <jackabt@amazon.com>

Author: JackThomson2

src/vmm/src/resources.rs

@@ -268,12 +268,6 @@ impl VmResources {
             return Err(MachineConfigError::IncompatibleBalloonSize);
         }
 
-        if self.balloon.get().is_some() && updated.secret_free {
-            return Err(MachineConfigError::Incompatible(
-                "balloon device",
-                "secret freedom",
-            ));
-        }
         if updated.secret_free {
             if self.vhost_user_devices_used() {
                 return Err(MachineConfigError::Incompatible(
@@ -347,10 +341,6 @@ impl VmResources {
             return Err(BalloonConfigError::TooManyPagesRequested);
         }
 
-        if self.machine_config.secret_free {
-            return Err(BalloonConfigError::IncompatibleWith("secret freedom"));
-        }
-
         self.balloon.set(config)
     }