KVM: nVMX: Fix using __this_cpu_read() in preemptible context

 BUG: using __this_cpu_read() in preemptible [00000000] code: qemu-system-x86/4590
  caller is nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
  CPU: 4 PID: 4590 Comm: qemu-system-x86 Tainted: G           OE     5.1.0-rc4+ #1
  Call Trace:
   dump_stack+0x67/0x95
   __this_cpu_preempt_check+0xd2/0xe0
   nested_vmx_enter_non_root_mode+0xebd/0x1790 [kvm_intel]
   nested_vmx_run+0xda/0x2b0 [kvm_intel]
   handle_vmlaunch+0x13/0x20 [kvm_intel]
   vmx_handle_exit+0xbd/0x660 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xa2c/0x1e50 [kvm]
   kvm_vcpu_ioctl+0x3ad/0x6d0 [kvm]
   do_vfs_ioctl+0xa5/0x6e0
   ksys_ioctl+0x6d/0x80
   __x64_sys_ioctl+0x1a/0x20
   do_syscall_64+0x6f/0x6c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Accessing per-cpu variable should disable preemption, this patch extends the
preemption disable region for __this_cpu_read().

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Fixes: 52017608 ("KVM: nVMX: add option to perform early consistency checks via H/W")
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>