kvm_mmu_unload() destroys all the PGD caches.  Use the lighter
kvm_mmu_sync_roots() and kvm_mmu_sync_prev_roots() instead.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-5-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>