$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-ysionneau1-9139-27959/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-ysionneau1-9139-27959/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 896caaacf23730a2c3024b7aa4770c779afa4464:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         896caaacf23730a2c3024b7aa4770c779afa4464 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 896caaa Merge pull request #60 from xcp-ng-rpms/Workaround-uncached-grant-table-on-AMD-cpus