Re: [PATCH v4 1/2] KVM: remove NULL return path for vcpu ids >= KVM_MAX_VCPUS

Gerg Kurz
2016-04-27T09:40:52Z

Quoting Greg Kurz <gkurz@linux.vnet.ibm.com>:

> Commit c896939f7cff ("KVM: use heuristic for fast VCPU lookup by id") added
> a return path that prevents vcpu ids to exceed KVM_MAX_VCPUS. This is a
> problem for powerpc where vcpu ids can grow up to 8*KVM_MAX_VCPUS.
>
> This patch simply reverses the logic so that we only try fast path if the
> vcpu id can be tried as an index in kvm->vcpus[]. The slow path is not
> affected by the change.
>
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---

Radim,

I think this sanity check is only needed because kvm_get_vcpu() use the
id as an index in kvm->vcpus[]. Checking against the new KVM_MAX_VCPU_ID
would be clearly wrong here.

And this patch got two R-b tags already. Do you agree we keep it ?

Cheers.

--
Greg

> include/linux/kvm_host.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 5276fe0916fc..23bfe1bd159c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -447,12 +447,13 @@ static inline struct kvm_vcpu
> *kvm_get_vcpu(struct kvm *kvm, int i)
>
> static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
> {
> - struct kvm_vcpu *vcpu;
> + struct kvm_vcpu *vcpu = NULL;
> int i;
>
> - if (id < 0 || id >= KVM_MAX_VCPUS)
> + if (id < 0)
> return NULL;
> - vcpu = kvm_get_vcpu(kvm, id);
> + if (id < KVM_MAX_VCPUS)
> + vcpu = kvm_get_vcpu(kvm, id);
> if (vcpu && vcpu->vcpu_id == id)
> return vcpu;
> kvm_for_each_vcpu(i, vcpu, kvm)
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html