KVM: nVMX: Fix mmu context after VMLAUNCH/VMRESUME failure

Commit 4f350c6d (kvm: nVMX: Handle deferred early VMLAUNCH/VMRESUME failure
properly) can result in L1(run kvm-unit-tests/run_tests.sh vmx_controls in L1)
null pointer deference and also L0 calltrace when EPT=0 on both L0 and L1.

In L1:

BUG: unable to handle kernel paging request at ffffffffc015bf8f
 IP: vmx_vcpu_run+0x202/0x510 [kvm_intel]
 PGD 146e13067 P4D 146e13067 PUD 146e15067 PMD 3d2686067 PTE 3d4af9161
 Oops: 0003 [#1] PREEMPT SMP
 CPU: 2 PID: 1798 Comm: qemu-system-x86 Not tainted 4.14.0-rc4+ #6
 RIP: 0010:vmx_vcpu_run+0x202/0x510 [kvm_intel]
 Call Trace:
 WARNING: kernel stack frame pointer at ffffb86f4988bc18 in qemu-system-x86:1798 has bad value 0000000000000002

In L0:

-----------[ cut here ]------------
 WARNING: CPU: 6 PID: 4460 at /home/kernel/linux/arch/x86/kvm//vmx.c:9845 vmx_inject_page_fault_nested+0x130/0x140 [kvm_intel]
 CPU: 6 PID: 4460 Comm: qemu-system-x86 Tainted: G           OE   4.14.0-rc7+ #25
 RIP: 0010:vmx_inject_page_fault_nested+0x130/0x140 [kvm_intel]
 Call Trace:
  paging64_page_fault+0x500/0xde0 [kvm]
  ? paging32_gva_to_gpa_nested+0x120/0x120 [kvm]
  ? nonpaging_page_fault+0x3b0/0x3b0 [kvm]
  ? __asan_storeN+0x12/0x20
  ? paging64_gva_to_gpa+0xb0/0x120 [kvm]
  ? paging64_walk_addr_generic+0x11a0/0x11a0 [kvm]
  ? lock_acquire+0x2c0/0x2c0
  ? vmx_read_guest_seg_ar+0x97/0x100 [kvm_intel]
  ? vmx_get_segment+0x2a6/0x310 [kvm_intel]
  ? sched_clock+0x1f/0x30
  ? check_chain_key+0x137/0x1e0
  ? __lock_acquire+0x83c/0x2420
  ? kvm_multiple_exception+0xf2/0x220 [kvm]
  ? debug_check_no_locks_freed+0x240/0x240
  ? debug_smp_processor_id+0x17/0x20
  ? __lock_is_held+0x9e/0x100
  kvm_mmu_page_fault+0x90/0x180 [kvm]
  kvm_handle_page_fault+0x15c/0x310 [kvm]
  ? __lock_is_held+0x9e/0x100
  handle_exception+0x3c7/0x4d0 [kvm_intel]
  vmx_handle_exit+0x103/0x1010 [kvm_intel]
  ? kvm_arch_vcpu_ioctl_run+0x1628/0x2e20 [kvm]

The commit avoids to load host state of vmcs12 as vmcs01's guest state
since vmcs12 is not modified (except for the VM-instruction error field)
if the checking of vmcs control area fails. However, the mmu context is
switched to nested mmu in prepare_vmcs02() and it will not be reloaded
since load_vmcs12_host_state() is skipped when nested VMLAUNCH/VMRESUME
fails. This patch fixes it by reloading mmu context when nested
VMLAUNCH/VMRESUME fails.

Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>