Revert "KVM: x86: use the fast way to invalidate all pages"

Revert "KVM: x86: use the fast way to invalidate all pages"

Revert to a slow kvm_mmu_zap_all() for kvm_arch_flush_shadow_all().
Flushing all shadow entries is only done during VM teardown, i.e.
kvm_arch_flush_shadow_all() is only called when the associated MM struct
is being released or when the VM instance is being freed.

Although the performance of teardown itself isn't critical, KVM should
still voluntarily schedule to play nice with the rest of the kernel;
but that can be done without the fast invalidate mechanism in a future
patch.

This reverts commit f085ba33c57e3b181f8bea34eb829eb4bab67dca.

Cc: Xiao Guangrong <guangrong.xiao@gmail.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>