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

Alexander Graf
2011-12-20T15:20:37Z

On 07.12.2011, at 08:19, Matt Evans 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. :)
>
>
> Cheers,
>
>
> Matt
>
> ---
> Subject: [PATCH] KVM: PPC: Fix vcpu_create dereference before validity check.
>
>
> Signed-off-by: Matt Evans <matt@ozlabs.org>

Thanks, applied to kvm-ppc-next with an actual patch description added.

Alex

> ---
> arch/powerpc/kvm/powerpc.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 084d1c5..7c7220c 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -285,9 +285,10 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
> {
> struct kvm_vcpu *vcpu;
> vcpu = kvmppc_core_vcpu_create(kvm, id);
> - vcpu->arch.wqp = &vcpu->wq;
> - if (!IS_ERR(vcpu))
> + if (!IS_ERR(vcpu)) {
> + vcpu->arch.wqp = &vcpu->wq;
> kvmppc_create_vcpu_debugfs(vcpu, id);
> + }
> return vcpu;
> }
>
> --
> 1.7.0.4
>