# \[PATCHv2 5/7\] KVM: PPC: Book3S HV nestedv2: reject vCPU ids beyond the PAPR limit - From: Ritesh Harjani (IBM) \ - Date: 2026-11-01 14:47:12 - List: linuxppc-dev - Page: https://ratatoskr.run/linuxppc-dev/2026/11/17839665 - Thread: https://ratatoskr.run/linuxppc-dev/2026/11/17839658/t.md ```text The previous patch caps KVM_CAP_MAX_VCPU_ID at 2048 on nestedv2 but nothing actually enforces it. The generic KVM_CREATE_VCPU path only checks the id against KVM_MAX_VCPU_IDS, which is 8 * NR_CPUS on HV. That means a VMM that ignores the capability can still pass a larger id. That id goes all the way down to H_GUEST_CREATE_VCPU, where the L0 rejects it and prints, ... KVM: Create Guest vcpu hcall failed, rc=-56 ...for every such attempt before failing the ioctl with -EINVAL anyway. Check the id in kvm_arch_vcpu_precreate() instead so it fails early with the same -EINVAL. Note that PowerNV and nestedv1 are not affected. Signed-off-by: Ritesh Harjani (IBM) --- arch/powerpc/kvm/powerpc.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index cf620b6534de..5f9cfc34bec2 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -778,6 +778,9 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm, int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id) { + if (kvmhv_is_nestedv2() && id >= KVM_MAX_VCPU_IDS_NESTEDv2) + return -EINVAL; + return 0; } -- 2.39.5 ```