From 47b56e7c19c2e3af685ee408f02f232efb3d12b1 Mon Sep 17 00:00:00 2001
From: Matthew Bauer <mjbauer95@gmail.com>
Date: Fri, 21 Aug 2020 23:33:59 -0500
Subject: [PATCH] runInLinuxVM, test-driver: use -cpu max instead of -cpu host
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This appears to avoid requiring KVM when it’s not available. This is
what I originally though -cpu host did. Unfortunately not much
documentation available from the QEMU side on this, but this appears
to square with help:

$ qemu-system-x86 -cpu help
...
x86 host                  KVM processor with all supported host features
x86 max                   Enables all features supported by the accelerator in the current host
...

Whether we actually want to support this not clear, since this only
happens when your CPU doesn’t have full KVM support. Some Nix builders
are lying about kvm support though. Things aren’t too slow without it
though.

Fixes https://github.com/NixOS/nixpkgs/issues/85394

Alternative to https://github.com/NixOS/nixpkgs/pull/83920
---
 nixos/lib/qemu-flags.nix  | 4 ++--
 nixos/tests/installer.nix | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/nixos/lib/qemu-flags.nix b/nixos/lib/qemu-flags.nix
index 0cf6977af4b..0f066245893 100644
--- a/nixos/lib/qemu-flags.nix
+++ b/nixos/lib/qemu-flags.nix
@@ -22,9 +22,9 @@ rec {
         else throw "Unknown QEMU serial device for system '${pkgs.stdenv.hostPlatform.system}'";
 
   qemuBinary = qemuPkg: {
-    x86_64-linux = "${qemuPkg}/bin/qemu-kvm -cpu host";
+    x86_64-linux = "${qemuPkg}/bin/qemu-kvm -cpu max";
     armv7l-linux = "${qemuPkg}/bin/qemu-system-arm -enable-kvm -machine virt -cpu host";
     aarch64-linux = "${qemuPkg}/bin/qemu-system-aarch64 -enable-kvm -machine virt,gic-version=host -cpu host";
-    x86_64-darwin = "${qemuPkg}/bin/qemu-kvm -cpu host";
+    x86_64-darwin = "${qemuPkg}/bin/qemu-kvm -cpu max";
   }.${pkgs.stdenv.hostPlatform.system} or "${qemuPkg}/bin/qemu-kvm";
 }
diff --git a/nixos/tests/installer.nix b/nixos/tests/installer.nix
index 02b839fee3f..420951eb715 100644
--- a/nixos/tests/installer.nix
+++ b/nixos/tests/installer.nix
@@ -74,7 +74,7 @@ let
       throw "Non-EFI boot methods are only supported on i686 / x86_64"
     else ''
       def assemble_qemu_flags():
-          flags = "-cpu host"
+          flags = "-cpu max"
           ${if system == "x86_64-linux"
             then ''flags += " -m 768"''
             else ''flags += " -m 512 -enable-kvm -machine virt,gic-version=host"''