Re: [PATCH] KVM: PPC: Book3S HV: Replace kvmppc_find_vcpu() with kvm_get_vcpu()

[Thomas Huth <thuth@redhat.com>]

On Fri, 8 May 2015 09:07:18 +1000
Paul Mackerras <paulus@samba.org> wrote:

> On Thu, May 07, 2015 at 05:49:39PM +0200, Thomas Huth wrote:
> > Both functions are doing the same thing - looking up the struct
> > kvm_vcpu pointer for a given vCPU ID.
> 
> No, kvm_get_vcpu(n) returns the n'th vcpu created, which is often
> but not necessarily the same as the vcpu with id n.  In fact, due to
> the way we do threading in HV KVM, it's quite common for userspace to
> create vcpus with ids 0, 8, 16, ..., which means that the n'th vcpu
> created does not have id n (except of course for vcpu 0).

Ah, ok, thanks a lot for the explanation ... I thought that KVM would
always put the VCPUs at the position of their ID into the array, but
looking at kvm_vm_ioctl_create_vcpu(), you're right, it's using the
amount of online CPUs as index instead:

	kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;

So never mind, and sorry for the nuisance!

 Thomas