linux-kernel - [PATCH v2] KVM: PPC: Enable CAP_SPAPR_TCE

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Message-ID: <20250129094033.2265211-1-amachhiw@linux.ibm.com>
Date: Wed, 29 Jan 2025 15:10:33 +0530
From: Amit Machhiwal <amachhiw@...ux.ibm.com>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc: Amit Machhiwal <amachhiw@...ux.ibm.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Shivaprasad G Bhat <sbhat@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Naveen N Rao <naveen@...nel.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH v2] 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.

Fix this by enabling the CAP_SPAPR_TCE_VFIO on the pSeries hosts as well
for the nested PAPR guests. With the patch, booting an L2 guest with
128G memory results in an average improvement of 11% in the startup
times.

Fixes: f431a8cde7f1 ("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries")
Cc: stable@...r.kernel.org
Signed-off-by: Amit Machhiwal <amachhiw@...ux.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: 6d61a53dd6f55405ebcaea6ee38d1ab5a8856c2c
-- 
2.48.1