KVM: x86/mmu: Treat NX as a valid SPTE bit for NPT

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2119111



commit 6c6ab524
Author: Sean Christopherson <seanjc@google.com>
Date:   Sat Jul 23 01:30:29 2022 +0000

    KVM: x86/mmu: Treat NX as a valid SPTE bit for NPT

    Treat the NX bit as valid when using NPT, as KVM will set the NX bit when
    the NX huge page mitigation is enabled (mindblowing) and trigger the WARN
    that fires on reserved SPTE bits being set.

    KVM has required NX support for SVM since commit b26a71a1 ("KVM: SVM:
    Refuse to load kvm_amd if NX support is not available") for exactly this
    reason, but apparently it never occurred to anyone to actually test NPT
    with the mitigation enabled.

      ------------[ cut here ]------------
      spte = 0x800000018a600ee7, level = 2, rsvd bits = 0x800f0000001fe000
      WARNING: CPU: 152 PID: 15966 at arch/x86/kvm/mmu/spte.c:215 make_spte+0x327/0x340 [kvm]
      Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 10.48.0 01/27/2022
      RIP: 0010:make_spte+0x327/0x340 [kvm]
      Call Trace:
       <TASK>
       tdp_mmu_map_handle_target_level+0xc3/0x230 [kvm]
       kvm_tdp_mmu_map+0x343/0x3b0 [kvm]
       direct_page_fault+0x1ae/0x2a0 [kvm]
       kvm_tdp_page_fault+0x7d/0x90 [kvm]
       kvm_mmu_page_fault+0xfb/0x2e0 [kvm]
       npf_interception+0x55/0x90 [kvm_amd]
       svm_invoke_exit_handler+0x31/0xf0 [kvm_amd]
       svm_handle_exit+0xf6/0x1d0 [kvm_amd]
       vcpu_enter_guest+0xb6d/0xee0 [kvm]
       ? kvm_pmu_trigger_event+0x6d/0x230 [kvm]
       vcpu_run+0x65/0x2c0 [kvm]
       kvm_arch_vcpu_ioctl_run+0x355/0x610 [kvm]
       kvm_vcpu_ioctl+0x551/0x610 [kvm]
       __se_sys_ioctl+0x77/0xc0
       __x64_sys_ioctl+0x1d/0x20
       do_syscall_64+0x44/0xa0
       entry_SYSCALL_64_after_hwframe+0x46/0xb0
       </TASK>
      ---[ end trace 0000000000000000 ]---

    Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
    Message-Id: <20220723013029.1753623-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>