[PATCH 0/1 v2] KVM: MMU: Use ptep_user for cmpxchg_gpte()

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

Changelog v1->v2:
  Added error handling for get_user_pages_fast() failure

Tested with NPT off:

  paging64_walk_addr_generic() {
    get_cr3();
    translate_gpa();
    gfn_to_hva();
    kvm_is_error_hva();
    _cond_resched();
    translate_gpa();
    gfn_to_hva();
    kvm_is_error_hva();
    _cond_resched();
    translate_gpa();
    gfn_to_hva();
    kvm_is_error_hva();
    _cond_resched();
    translate_gpa();
    gfn_to_hva();
    kvm_is_error_hva();
    _cond_resched();
    paging64_cmpxchg_gpte() {
      get_user_pages_fast() {
        gup_pud_range() {
          gup_pte_range();
        }
      }
      kvm_release_page_dirty() {
        kvm_release_pfn_dirty() {
          kvm_set_pfn_dirty();
          kvm_release_pfn_clean() {
            put_page();
          }
        }
      }
    }
    mark_page_dirty();
    translate_gpa();
  }