[PATCH 2/3] KVM: nVMX: restore L1's EFER prior to setting the nested state

[Maxim Levitsky]

It is known that some kvm's users (e.g. qemu) load part of L2's register
state prior to setting the nested state after a migration.

If a 32 bit L2 guest is running in a 64 bit L1 guest, and nested migration
happens, Qemu will restore L2's EFER, and then the nested state load
function will use it as if it was L1's EFER.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 49ae96c0cc4d1..28e270824e5b1 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6404,6 +6404,17 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 			kvm_state->hdr.vmx.preemption_timer_deadline;
 	}
 
+	/*
+	 * The vcpu might currently contain L2's IA32_EFER, due to the way
+	 * some userspace kvm users (e.g qemu) restore nested state.
+	 *
+	 * To fix this, restore its IA32_EFER to the value it would have
+	 * after VM exit from the nested guest.
+	 *
+	 */
+
+	vcpu->arch.efer = nested_vmx_get_vmcs12_host_efer(vcpu, vmcs12);
+
 	if (nested_vmx_check_controls(vcpu, vmcs12) ||
 	    nested_vmx_check_host_state(vcpu, vmcs12) ||
 	    nested_vmx_check_guest_state(vcpu, vmcs12, &ignored))
-- 
2.26.3