[PATCH v3] KVM: PPC: Enable CAP_SPAPR_TCE_VFIO on pSeries KVM guests

[Amit Machhiwal]

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 f431a8cde7f1
("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: f431a8cde7f1 ("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries")
Cc: stable at vger.kernel.org
Reviewed-by: Vaibhav Jain <vaibhav at linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list at gmail.com>
Signed-off-by: Amit Machhiwal <amachhiw at linux.ibm.com>
---
Changes since v2:
    * Updated the patch description
    * v2: https://lore.kernel.org/all/20250129094033.2265211-1-amachhiw@linux.ibm.com/
Changes since v1:
    * Addressed review comments from Ritesh
    * v1: https://lore.kernel.org/all/20250109132053.158436-1-amachhiw@linux.ibm.com/

 arch/powerpc/kvm/powerpc.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index ce1d91eed231..a7138eb18d59 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -543,26 +543,23 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = !hv_enabled;
 		break;
 #ifdef CONFIG_KVM_MPIC
 	case KVM_CAP_IRQ_MPIC:
 		r = 1;
 		break;
 #endif
 
 #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:
 #ifdef CONFIG_KVM_XICS
 	case KVM_CAP_IRQ_XICS:
 #endif
 	case KVM_CAP_PPC_GET_CPU_CHAR:
 		r = 1;
 		break;
 #ifdef CONFIG_KVM_XIVE

base-commit: 6537cfb395f352782918d8ee7b7f10ba2cc3cbf2
-- 
2.48.1