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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Fri, 23 Apr 2021 17:46:03 -0700
In-Reply-To: <20210424004645.3950558-1-seanjc@google.com>
Message-Id: <20210424004645.3950558-2-seanjc@google.com>
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Subject: [PATCH 01/43] KVM: nVMX: Set LDTR to its architecturally defined
 value on nested VM-Exit
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Precedence: bulk

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")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/nested.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 00339d624c92..32126fa0c4d8 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4276,6 +4276,10 @@ 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);
 
-- 
2.31.1.498.g6c1eba8ee3d-goog