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 @@ -2392,6 +2392,16 @@ 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 @@ -2878,6 +2878,7 @@ 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;
@@ -2894,15 +2895,18 @@ 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)