KVM: nVMX: Don't clobber nested MMU's A/D status on EPTP switch

Drop bogus logic that incorrectly clobbers the accessed/dirty enabling
status of the nested MMU on an EPTP switch.  When nested EPT is enabled,
walk_mmu points at L2's _legacy_ page tables, not L1's EPT for L2.

This is likely a benign bug, as mmu->ept_ad is never consumed (since the
MMU is not a nested EPT MMU), and stuffing mmu_role.base.ad_disabled will
never propagate into future shadow pages since the nested MMU isn't used
to map anything, just to walk L2's page tables.

Note, KVM also does a full MMU reload, i.e. the guest_mmu will be
recreated using the new EPTP, and thus any change in A/D enabling will be
properly recognized in the relevant MMU.

Fixes: 41ab93727467 ("KVM: nVMX: Emulate EPTP switching for the L1 hypervisor")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 775df9e..7210e7c 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5546,8 +5546,6 @@ static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
 {
        u32 index = kvm_rcx_read(vcpu);
        u64 new_eptp;
-       bool accessed_dirty;
-       struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
 
        if (!nested_cpu_has_eptp_switching(vmcs12) ||
            !nested_cpu_has_ept(vmcs12))
@@ -5556,13 +5554,10 @@ static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
        if (index >= VMFUNC_EPTP_ENTRIES)
                return 1;
 
-
        if (kvm_vcpu_read_guest_page(vcpu, vmcs12->eptp_list_address >> PAGE_SHIFT,
                                     &new_eptp, index * 8, 8))
                return 1;
 
-       accessed_dirty = !!(new_eptp & VMX_EPTP_AD_ENABLE_BIT);
-
        /*
         * If the (L2) guest does a vmfunc to the currently
         * active ept pointer, we don't have to do anything else
@@ -5571,8 +5566,6 @@ static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
                if (!nested_vmx_check_eptp(vcpu, new_eptp))
                        return 1;
 
-               mmu->ept_ad = accessed_dirty;
-               mmu->mmu_role.base.ad_disabled = !accessed_dirty;
                vmcs12->ept_pointer = new_eptp;
 
                kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);