test: use QEMU from stable nixpkgs

test/lib/make-test-vm.nix

@@ -3,11 +3,6 @@ testArgs:
 let
   pkgs = import <nixpkgs> { config = {}; overlays = []; };
 
-  pkgs19_09 = import (pkgs.fetchzip {
-    url = "https://github.com/NixOS/nixpkgs-channels/archive/a7ceb2536ab11973c59750c4c48994e3064a75fa.tar.gz";
-    sha256 = "0hka65f31njqpq7i07l22z5rs7lkdfcl4pbqlmlsvnysb74ynyg1";
-  }) { config = {}; overlays = []; };
-
   test = (import "${pkgs.path}/nixos/tests/make-test-python.nix") testArgs;
 
   fixedTest = { system ? builtins.currentSystem, ... }@args:
@@ -23,11 +18,6 @@ let
              exec ${pkgs.python3Packages.black}/bin/black $extraArgs "$@"
            '';
          };
-
-         # QEMU 4.20 from unstable fails on Travis build nodes with message
-         # "error: failed to set MSR 0x48b to 0x159ff00000000"
-         # Use version 4.0.1 instead.
-         inherit (pkgs19_09) qemu_test;
        };
     in
       test (args // { pkgs = pkgsFixed; });

test/run-tests.sh

@@ -149,14 +149,19 @@ exprForCI() {
     ((memAvailableMiB < memoryMiB)) && memoryMiB=$memAvailableMiB
     >&2 echo "VM stats: CPUs: $numCPUs, memory: $memoryMiB MiB"
     >&2 echo "Host memory total: $((memTotalKiB / 1024)) MiB, available: $memAvailableMiB MiB"
-    vmTestNixExpr
+
+    # VMX is usually not available on CI nodes due to recursive virtualisation.
+    # Explicitly disable VMX, otherwise QEMU 4.20 fails with message
+    # "error: failed to set MSR 0x48b to 0x159ff00000000"
+    vmTestNixExpr "-cpu host,-vmx"
 }
 
 vmTestNixExpr() {
+  extraQEMUOpts="$1"
   cat <<EOF
     ((import "$testDir/tests.nix" { scenario = "$scenario"; }).vm {}).overrideAttrs (old: rec {
       buildCommand = ''
-        export QEMU_OPTS="-smp $numCPUs -m $memoryMiB"
+        export QEMU_OPTS="-smp $numCPUs -m $memoryMiB $extraQEMUOpts"
         echo "VM stats: CPUs: $numCPUs, memory: $memoryMiB MiB"
       '' + old.buildCommand;
     })