KVM: PPC: Book3S HV: Don't access HFSCR, LPIDR or LPCR when running nested

When running as a nested hypervisor, this avoids reading hypervisor
privileged registers (specifically HFSCR, LPIDR and LPCR) at startup;
instead reasonable default values are used.  This also avoids writing
LPIDR in the single-vcpu entry/exit path.

Also, this removes the check for CPU_FTR_HVMODE in kvmppc_mmu_hv_init()
since its only caller already checks this.
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -268,13 +268,12 @@ int kvmppc_mmu_hv_init(void)
 {
 	unsigned long host_lpid, rsvd_lpid;
 
-	if (!cpu_has_feature(CPU_FTR_HVMODE))
-		return -EINVAL;
-
 	if (!mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE))
 		return -EINVAL;
 
 	/* POWER7 has 10-bit LPIDs (12-bit in POWER8) */
+	host_lpid = 0;
+	if (cpu_has_feature(CPU_FTR_HVMODE))
 		host_lpid = mfspr(SPRN_LPID);
 	rsvd_lpid = LPID_RSVD;
 

arch/powerpc/kvm/book3s_hv.c

@@ -2174,15 +2174,18 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
 	 * Set the default HFSCR for the guest from the host value.
 	 * This value is only used on POWER9.
 	 * On POWER9, we want to virtualize the doorbell facility, so we
-	 * turn off the HFSCR bit, which causes those instructions to trap.
+	 * don't set the HFSCR_MSGP bit, and that causes those instructions
+	 * to trap and then we emulate them.
 	 */
-	vcpu->arch.hfscr = mfspr(SPRN_HFSCR);
+	vcpu->arch.hfscr = HFSCR_TAR | HFSCR_EBB | HFSCR_PM | HFSCR_BHRB |
+		HFSCR_DSCR | HFSCR_VECVSX | HFSCR_FP;
+	if (cpu_has_feature(CPU_FTR_HVMODE)) {
+		vcpu->arch.hfscr &= mfspr(SPRN_HFSCR);
 		if (cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
 			vcpu->arch.hfscr |= HFSCR_TM;
-	else if (!cpu_has_feature(CPU_FTR_TM_COMP))
-		vcpu->arch.hfscr &= ~HFSCR_TM;
-	if (cpu_has_feature(CPU_FTR_ARCH_300))
-		vcpu->arch.hfscr &= ~HFSCR_MSGP;
+	}
+	if (cpu_has_feature(CPU_FTR_TM_COMP))
+		vcpu->arch.hfscr |= HFSCR_TM;
 
 	kvmppc_mmu_book3s_hv_init(vcpu);
 
@@ -4006,8 +4009,10 @@ int kvmhv_run_single_vcpu(struct kvm_run *kvm_run,
 
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 
+	if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		mtspr(SPRN_LPID, kvm->arch.host_lpid);
 		isync();
+	}
 
 	trace_hardirqs_off();
 	set_irq_happened(trap);
@@ -4634,9 +4639,13 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
 		kvm->arch.host_sdr1 = mfspr(SPRN_SDR1);
 
 	/* Init LPCR for virtual RMA mode */
+	if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		kvm->arch.host_lpid = mfspr(SPRN_LPID);
 		kvm->arch.host_lpcr = lpcr = mfspr(SPRN_LPCR);
 		lpcr &= LPCR_PECE | LPCR_LPES;
+	} else {
+		lpcr = 0;
+	}
 	lpcr |= (4UL << LPCR_DPFD_SH) | LPCR_HDICE |
 		LPCR_VPM0 | LPCR_VPM1;
 	kvm->arch.vrma_slb_v = SLB_VSID_B_1T |