Re: [PATCH v3 30/33] KVM: PPC: Book3S HV: Allow HV module to load without hypervisor mode

With this, the KVM-HV module can be loaded in a guest running under
KVM-HV, and if the hypervisor supports nested virtualization, this
guest can now act as a nested hypervisor and run nested guests.

This also adds some checks to inform userspace that HPT guests are not
supported by nested hypervisors, and to prevent userspace from
configuring a guest to use HPT mode.

Signed-off-by: Paul Mackerras <redacted>
---
 arch/powerpc/kvm/book3s_hv.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index f630e91..196bff1 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -4237,6 +4237,10 @@ static int kvm_vm_ioctl_get_smmu_info_hv(struct kvm *kvm,
 {
 	struct kvm_ppc_one_seg_page_size *sps;
 
+	/* If we're a nested hypervisor, we only support radix guests */
+	if (kvmhv_on_pseries())
+		return -EINVAL;
+
 	/*
 	 * POWER7, POWER8 and POWER9 all support 32 storage keys for data.
 	 * POWER7 doesn't support keys for instruction accesses,

@@ -4822,11 +4826,15 @@ static int kvmppc_core_emulate_mfspr_hv(struct kvm_vcpu *vcpu, int sprn,
 
 static int kvmppc_core_check_processor_compat_hv(void)
 {
-	if (!cpu_has_feature(CPU_FTR_HVMODE) ||
-	    !cpu_has_feature(CPU_FTR_ARCH_206))
-		return -EIO;
+	if (cpu_has_feature(CPU_FTR_HVMODE) &&
+	    cpu_has_feature(CPU_FTR_ARCH_206))
+		return 0;
 
-	return 0;
+	/* Can run as nested hypervisor on POWER9 in radix mode. */
+	if (cpu_has_feature(CPU_FTR_ARCH_300) && radix_enabled())

+		return 0;
+
+	return -EIO;
 }
 
 #ifdef CONFIG_KVM_XICS

@@ -5144,6 +5152,10 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
 	if (radix && !radix_enabled())
 		return -EINVAL;
 
+	/* If we're a nested hypervisor, we currently only support radix */
+	if (kvmhv_on_pseries() && !radix)
+		return -EINVAL;
+
 	mutex_lock(&kvm->lock);
 	if (radix != kvm_is_radix(kvm)) {
 		if (kvm->arch.mmu_ready) {