Commit 272b0a99 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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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: 41ab9372 ("KVM: nVMX: Emulate EPTP switching for the L1 hypervisor")
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-4-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0e75225d

arch/x86/kvm/vmx/nested.c

+0 −7
Original line number Diff line number Diff line
@@ -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);