KVM: nVMX: Set LDTR to its architecturally defined value on nested VM-Exit

Set L1's LDTR on VM-Exit per the Intel SDM:

  The host-state area does not contain a selector field for LDTR. LDTR is
  established as follows on all VM exits: the selector is cleared to
  0000H, the segment is marked unusable and is otherwise undefined
  (although the base address is always canonical).

This is likely a benign bug since the LDTR is unusable, as it means the
L1 VMM is conditioned to reload its LDTR in order to function properly on
bare metal.

Fixes: 4704d0befb07 ("KVM: nVMX: Exiting from L2 to L1")
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-3-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 1a52134..7f8184f 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4298,6 +4298,10 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
        };
        vmx_set_segment(vcpu, &seg, VCPU_SREG_TR);
 
+       memset(&seg, 0, sizeof(seg));
+       seg.unusable = 1;
+       vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR);
+
        kvm_set_dr(vcpu, 7, 0x400);
        vmcs_write64(GUEST_IA32_DEBUGCTL, 0);