Re: [PATCH 07/28] kvm tools: Move 'kvm__recommended_cpus' to

Sasha Levin
2011-12-07T06:34:55Z

On Wed, 2011-12-07 at 17:17 +1100, Matt Evans wrote:
> On 06/12/11 19:20, Sasha Levin wrote:
> > Why is it getting moved out of generic code?
> >
> > This is used to determine the maximum amount of vcpus supported by the
> > host for a single guest, and as far as I know KVM_CAP_NR_VCPUS and
> > KVM_CAP_MAX_VCPUS are not arch specific.
>
> I checked api.txt and you're right, it isn't arch-specific. I assumed it was,
> because PPC KVM doesn't support it ;-) I've dropped this patch and in its place
> implemented the api.txt suggestion of "if KVM_CAP_NR_VCPUS fails, use 4" instead
> of die(); you'll see that when I repost.
>
> This will have the effect of PPC being limited to 4 CPUs until the kernel
> supports that CAP. (I'll see about this part too.)

I went to look at which limitation PPC places on amount of vcpus in
guest, and saw this in kvmppc_core_vcpu_create() in the book3s code:

vcpu = kvmppc_core_vcpu_create(kvm, id);
vcpu->arch.wqp = &vcpu->wq;
if (!IS_ERR(vcpu))
kvmppc_create_vcpu_debugfs(vcpu, id);

This is wrong, right? The VCPU is dereferenced before actually checking
that it's not an error.

--

Sasha.