KVM: PPC: Book3S HV: Ensure MSR[HV] is always clear in guest MSR

Rather than clear the HV bit from the MSR at guest entry, make it clear
that the hypervisor does not allow the guest to set the bit.

The HV clear is kept in guest entry for now, but a future patch will
warn if it is set.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210412014845.1517916-13-npiggin@gmail.com

arch/powerpc/kvm/book3s_hv_builtin.c

@@ -662,8 +662,8 @@ static void kvmppc_end_cede(struct kvm_vcpu *vcpu)
 
 void kvmppc_set_msr_hv(struct kvm_vcpu *vcpu, u64 msr)
 {
-	/* Guest must always run with ME enabled. */
-	msr = msr | MSR_ME;
+	/* Guest must always run with ME enabled, HV disabled. */
+	msr = (msr | MSR_ME) & ~MSR_HV;
 
 	/*
 	 * Check for illegal transactional state bit combination

arch/powerpc/kvm/book3s_hv_nested.c

@@ -344,8 +344,8 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
 	vcpu->arch.nested_vcpu_id = l2_hv.vcpu_token;
 	vcpu->arch.regs = l2_regs;
 
-	/* Guest must always run with ME enabled. */
-	vcpu->arch.shregs.msr = vcpu->arch.regs.msr | MSR_ME;
+	/* Guest must always run with ME enabled, HV disabled. */
+	vcpu->arch.shregs.msr = (vcpu->arch.regs.msr | MSR_ME) & ~MSR_HV;
 
 	sanitise_hv_regs(vcpu, &l2_hv);
 	restore_hv_regs(vcpu, &l2_hv);