fix(test): Remove flush_l1d from host-guest feature diff on ubuntu

Linux kernel v6.4+ passes through the "l1d_flush" CPUID bit to guests.
While our ubuntu host kernel is 6.8 that has the change, the latest
Amazon Linux 2 and Amazon Linux 2023 haven't.

Fixes: 4e014a1 ("test(x86_64): add host vs guest cpu feature test")
Signed-off-by: Takahiro Itazuri <[email protected]>

tests/integration_tests/functional/test_cpu_features_x86_64.py

@@ -343,7 +343,7 @@ def test_host_vs_guest_cpu_features_x86_64(uvm_nano):
                 "umip",
             }
         case CpuModel.INTEL_CASCADELAKE:
-            assert host_feats - guest_feats == {
+            expected = {
                 "acpi",
                 "aperfmperf",
                 "arch_perfmon",
@@ -392,6 +392,15 @@ def test_host_vs_guest_cpu_features_x86_64(uvm_nano):
                 "vpid",
                 "xtpr",
             }
+            # TODO: Remove the below ubuntu exception and "flush_l1d" from the above expected list
+            # once Amazon Linux 2 and Amazon Linux 2023 picks the following kernel commit and passes
+            # through the "flush_l1d" CPUID bit to guests.
+            # https://github.com/torvalds/linux/commit/45cf86f26148e549c5ba4a8ab32a390e4bde216e
+            # See also https://github.com/firecracker-microvm/firecracker/issues/4899
+            if "Ubuntu" in global_props.os:
+                expected -= {"flush_l1d"}
+            assert host_feats - guest_feats == expected
+
             assert guest_feats - host_feats == {
                 "hypervisor",
                 "tsc_known_freq",