From 86a35e97d286cbb6e23f8cc7bec5a05f022da0cb Mon Sep 17 00:00:00 2001
From: Artom Lifshitz <alifshit@redhat.com>
Date: Tue, 31 Oct 2023 22:52:50 -0400
Subject: [PATCH] libvirt: Stop unconditionally enabling evmcs

In I008841988547573878c4e06e82f0fa55084e51b5 we started enabling a
bunch of libvirt enlightenments for Windows unconditionally. Turns
out, the `evmcs` enlightenment only works on Intel hosts, and we broke
the ability to run Windows guests on AMD machines. Until we become
smarter about conditionally enabling evmcs (with something like traits
for host CPU features), just stop enabling it at all.

Change-Id: I2ff4fdecd9dc69de283f0e52e07df1aeaf0a9048
Closes-bug: 2009280
---
 nova/tests/unit/virt/libvirt/test_driver.py               | 5 ++++-
 nova/virt/libvirt/driver.py                               | 1 -
 ...p-unconditionally-enabling-evmcs-993a825641c4b9f3.yaml | 8 ++++++++
 3 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 releasenotes/notes/libvirt-enlightenments-stop-unconditionally-enabling-evmcs-993a825641c4b9f3.yaml

diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index d01b9c2677..ebba604ffa 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -27972,7 +27972,10 @@ class LibvirtDriverTestCase(test.NoDBTestCase, TraitsComparisonMixin):
         self.assertTrue(hv.reenlightenment)
         self.assertTrue(hv.tlbflush)
         self.assertTrue(hv.ipi)
-        self.assertTrue(hv.evmcs)
+        # NOTE(artom) evmcs only works on Intel hosts, so we can't enable it
+        # unconditionally. Until we become smarter about it, just don't enable
+        # it at all. See bug 2009280.
+        self.assertFalse(hv.evmcs)
 
 
 class LibvirtVolumeUsageTestCase(test.NoDBTestCase):
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index d03dc5fd67..1b28e50355 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -6234,7 +6234,6 @@ class LibvirtDriver(driver.ComputeDriver):
             hv.reenlightenment = True
             hv.tlbflush = True
             hv.ipi = True
-            hv.evmcs = True
 
             # NOTE(kosamara): Spoofing the vendor_id aims to allow the nvidia
             # driver to work on windows VMs. At the moment, the nvidia driver
diff --git a/releasenotes/notes/libvirt-enlightenments-stop-unconditionally-enabling-evmcs-993a825641c4b9f3.yaml b/releasenotes/notes/libvirt-enlightenments-stop-unconditionally-enabling-evmcs-993a825641c4b9f3.yaml
new file mode 100644
index 0000000000..31609f2a2d
--- /dev/null
+++ b/releasenotes/notes/libvirt-enlightenments-stop-unconditionally-enabling-evmcs-993a825641c4b9f3.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Bug 2009280 has been fixed by no longer enabling the evmcs enlightenment in
+    the libvirt driver. evmcs only works on Intel CPUs, and domains with that
+    enlightenment cannot be started on AMD hosts. There is a possible future
+    feature to enable support for generating this enlightenment only when
+    running on Intel hosts.