KVM: SVM: Don't allow nested guest to VMMCALL into host

This patch disables the possibility for a l2-guest to do a
VMMCALL directly into the host. This would happen if the
l1-hypervisor doesn't intercept VMMCALL and the l2-guest
executes this instruction.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/svm.c

@@ -2036,6 +2036,9 @@ static bool nested_svm_vmrun(struct vcpu_svm *svm)
 		svm->vmcb->control.intercept_cr_write &= ~INTERCEPT_CR8_MASK;
 	}
 
+	/* We don't want to see VMMCALLs from a nested guest */
+	svm->vmcb->control.intercept &= ~(1ULL << INTERCEPT_VMMCALL);
+
 	/*
 	 * We don't want a nested guest to be more powerful than the guest, so
 	 * all intercepts are ORed