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    Subject[PATCH 5.4 62/92] KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter
    Date
    From: Sean Christopherson <sean.j.christopherson@intel.com>

    commit 04f11ef45810da5ae2542dd78cc353f3761bd2cb upstream.

    Write the desired L2 CR3 into vmcs02.GUEST_CR3 during nested VM-Enter
    instead of deferring the VMWRITE until vmx_set_cr3(). If the VMWRITE
    is deferred, then KVM can consume a stale vmcs02.GUEST_CR3 when it
    refreshes vmcs12->guest_cr3 during nested_vmx_vmexit() if the emulated
    VM-Exit occurs without actually entering L2, e.g. if the nested run
    is squashed because nested VM-Enter (from L1) is putting L2 into HLT.

    Note, the above scenario can occur regardless of whether L1 is
    intercepting HLT, e.g. L1 can intercept HLT and then re-enter L2 with
    vmcs.GUEST_ACTIVITY_STATE=HALTED. But practically speaking, a VMM will
    likely put a guest into HALTED if and only if it's not intercepting HLT.

    In an ideal world where EPT *requires* unrestricted guest (and vice
    versa), VMX could handle CR3 similar to how it handles RSP and RIP,
    e.g. mark CR3 dirty and conditionally load it at vmx_vcpu_run(). But
    the unrestricted guest silliness complicates the dirty tracking logic
    to the point that explicitly handling vmcs02.GUEST_CR3 during nested
    VM-Enter is a simpler overall implementation.

    Cc: stable@vger.kernel.org
    Reported-and-tested-by: Reto Buerki <reet@codelabs.ch>
    Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    Reviewed-by: Liran Alon <liran.alon@oracle.com>
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Reviewed-by: Jim Mattson <jmattson@google.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kvm/vmx/nested.c | 10 ++++++++++
    arch/x86/kvm/vmx/vmx.c | 10 +++++++---
    2 files changed, 17 insertions(+), 3 deletions(-)

    --- a/arch/x86/kvm/vmx/nested.c
    +++ b/arch/x86/kvm/vmx/nested.c
    @@ -2418,6 +2418,16 @@ static int prepare_vmcs02(struct kvm_vcp
    entry_failure_code))
    return -EINVAL;

    + /*
    + * Immediately write vmcs02.GUEST_CR3. It will be propagated to vmcs12
    + * on nested VM-Exit, which can occur without actually running L2 and
    + * thus without hitting vmx_set_cr3(), e.g. if L1 is entering L2 with
    + * vmcs12.GUEST_ACTIVITYSTATE=HLT, in which case KVM will intercept the
    + * transition to HLT instead of running L2.
    + */
    + if (enable_ept)
    + vmcs_writel(GUEST_CR3, vmcs12->guest_cr3);
    +
    /* Late preparation of GUEST_PDPTRs now that EFER and CRs are set. */
    if (load_guest_pdptrs_vmcs12 && nested_cpu_has_ept(vmcs12) &&
    is_pae_paging(vcpu)) {
    --- a/arch/x86/kvm/vmx/vmx.c
    +++ b/arch/x86/kvm/vmx/vmx.c
    @@ -2995,6 +2995,7 @@ u64 construct_eptp(struct kvm_vcpu *vcpu
    void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
    {
    struct kvm *kvm = vcpu->kvm;
    + bool update_guest_cr3 = true;
    unsigned long guest_cr3;
    u64 eptp;

    @@ -3011,15 +3012,18 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu,
    spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
    }

    - if (enable_unrestricted_guest || is_paging(vcpu) ||
    - is_guest_mode(vcpu))
    + /* Loading vmcs02.GUEST_CR3 is handled by nested VM-Enter. */
    + if (is_guest_mode(vcpu))
    + update_guest_cr3 = false;
    + else if (enable_unrestricted_guest || is_paging(vcpu))
    guest_cr3 = kvm_read_cr3(vcpu);
    else
    guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
    ept_load_pdptrs(vcpu);
    }

    - vmcs_writel(GUEST_CR3, guest_cr3);
    + if (update_guest_cr3)
    + vmcs_writel(GUEST_CR3, guest_cr3);
    }

    int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)

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