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

Matt Evans
2011-12-07T07:19:42Z

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>
---
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