KVM: PPC: Enable CAP_SPAPR_TCE_VFIO on pSeries KVM guests

Currently on book3s-hv, the capability KVM_CAP_SPAPR_TCE_VFIO is only
available for KVM Guests running on PowerNV and not for the KVM guests
running on pSeries hypervisors. This prevents a pSeries L2 guest from
leveraging the in-kernel acceleration for H_PUT_TCE_INDIRECT and
H_STUFF_TCE hcalls that results in slow startup times for large memory
guests.

Support for VFIO on pSeries was restored in commit f431a8c
("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries"),
making it possible to re-enable this capability on pSeries hosts.

This change enables KVM_CAP_SPAPR_TCE_VFIO for nested PAPR guests on
pSeries, while maintaining the existing behavior on PowerNV. Booting an
L2 guest with 128GB of memory shows an average 11% improvement in
startup time.

Fixes: f431a8c ("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries")
Cc: stable@vger.kernel.org
Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250220070002.1478849-1-amachhiw@linux.ibm.com

Author: Amit Machhiwal

arch/powerpc/kvm/powerpc.c

@@ -550,12 +550,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 
 #ifdef CONFIG_PPC_BOOK3S_64
 	case KVM_CAP_SPAPR_TCE:
+		fallthrough;
 	case KVM_CAP_SPAPR_TCE_64:
-		r = 1;
-		break;
 	case KVM_CAP_SPAPR_TCE_VFIO:
-		r = !!cpu_has_feature(CPU_FTR_HVMODE);
-		break;
 	case KVM_CAP_PPC_RTAS:
 	case KVM_CAP_PPC_FIXUP_HCALL:
 	case KVM_CAP_PPC_ENABLE_HCALL: