[SRU][O][PATCH 1/1] KVM: PPC: Enable CAP_SPAPR_TCE_VFIO on pSeries KVM guests

[Massimiliano Pellizzer]

From: Amit Machhiwal <amachhiw at linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/2104893

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>
Signed-off-by: Madhavan Srinivasan <maddy at linux.ibm.com>
Link: https://patch.msgid.link/20250220070002.1478849-1-amachhiw@linux.ibm.com
(cherry picked from commit b4392813bbc3b05fc01a33c64d8b8c6c62c32cfa linux-next)
Signed-off-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.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 5e6c7b527677..92eef3659bab 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/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:
-- 
2.43.0