[PATCHv3 5/7] KVM: PPC: Book3S HV nestedv2: reject vCPU ids beyond the PAPR limit

[Ritesh Harjani (IBM)]

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) <ritesh.list@xxxxxxxxx>
---
 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