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

Matt Evans
2011-12-07T07:28:14Z

On 07/12/11 18:24, Alexander Graf wrote:
>
> On 07.12.2011, at 08:19, Matt Evans <matt@ozlabs.org> wrote:
>
>> On 07/12/11 17:34, Sasha Levin wrote:
>>> 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.
>>
>> Yeah, that's b0rk. Alex, a patch below. :)
>
> Thanks :). Will apply asap but don't have a real keyboard today :).

Ha! Voice control on your phone, what could go wrong?

> I suppose this is stable material?

Good idea, (and if we're formal,
Signed-off-by: Matt Evans <matt@ozlabs.org>
). I suppose no one's seen a vcpu fail to be created, yet.

Thanks,

Matt