anaconda: add smt=off xen option during installation

Defaults set during package installation do not apply, as booloader
configuration doesn't exist at that stage yet.

Reported by @rustybird
QubesOS/qubes-issues#4252

pyanaconda/bootloader.py

@@ -1535,7 +1535,7 @@ def write_defaults(self):
         # boot arguments
         log.info("bootloader.py: used boot args: %s ", self.boot_args)
         defaults.write("GRUB_CMDLINE_LINUX=\"%s\"\n" % self.boot_args)
-        defaults.write("GRUB_CMDLINE_XEN_DEFAULT=\"console=none dom0_mem=min:1024M dom0_mem=max:4096M iommu=no-igfx ucode=scan\"\n")
+        defaults.write("GRUB_CMDLINE_XEN_DEFAULT=\"console=none dom0_mem=min:1024M dom0_mem=max:4096M iommu=no-igfx ucode=scan smt=off\"\n")
         defaults.write("GRUB_DISABLE_RECOVERY=\"true\"\n")
         defaults.write("GRUB_THEME=\"/boot/grub2/themes/system/theme.txt\"\n")
         defaults.close()
@@ -1978,7 +1978,7 @@ def write_config_images(self, config):
                 root_args += " rootflags=subvol=%s" % image.device.name
             config.write("\n")
             config.write("[{}]\n".format(image.version))
-            config.write("options=loglvl=all dom0_mem=min:1024M dom0_mem=max:4096M iommu=no-igfx ucode=scan\n")
+            config.write("options=loglvl=all dom0_mem=min:1024M dom0_mem=max:4096M iommu=no-igfx ucode=scan smt=off\n")
             config.write("kernel={} {} {}\n".format(
                 image.kernel,
                 root_args,