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

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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: 41ab937274 ("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>
This commit is contained in:
Sean Christopherson 2021-06-09 16:42:23 -07:00 committed by Paolo Bonzini
parent 0e75225dfa
commit 272b0a998d
1 changed files with 0 additions and 7 deletions
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7
arch/x86/kvm/vmx/nested.c
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@ -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);