Re: [PATCH v5 2/2] kvm: introduce KVM_MAX_VCPU_ID

[Greg Kurz]

On Tue, 3 May 2016 08:49:12 +0200
Cornelia Huck <cornelia.huck@xxxxxxxxxx> wrote:

> On Tue, 03 May 2016 06:52:02 +0200
> Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > The KVM_MAX_VCPUS define provides the maximum number of vCPUs per guest, and
> > also the upper limit for vCPU ids. This is okay for all archs except PowerPC
> > which can have higher ids, depending on the cpu/core/thread topology. In the
> > worst case (single threaded guest, host with 8 threads per core), it limits
> > the maximum number of vCPUS to KVM_MAX_VCPUS / 8.
> > 
> > This patch separates the vCPU numbering from the total number of vCPUs, with
> > the introduction of KVM_MAX_VCPU_ID, as the maximal valid value for vCPU ids
> > plus one.
> > 
> > The corresponding KVM_CAP_MAX_VCPU_ID allows userspace to validate vCPU ids
> > before passing them to KVM_CREATE_VCPU.
> > 
> > Only PowerPC gets unlimited vCPU ids for the moment. This patch doesn't
> > change anything for other archs.
> > 
> > Suggested-by: Radim Krcmar <rkrcmar@xxxxxxxxxx>
> > Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx>
> > ---
> >  Documentation/virtual/kvm/api.txt   |   10 ++++++++--
> >  arch/powerpc/include/asm/kvm_host.h |    2 ++
> >  arch/powerpc/kvm/powerpc.c          |    3 +++
> >  include/linux/kvm_host.h            |    4 ++++
> >  include/uapi/linux/kvm.h            |    1 +
> >  virt/kvm/kvm_main.c                 |    2 +-
> >  6 files changed, 19 insertions(+), 3 deletions(-)
> >   
> 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 23bfe1bd159c..3b4efa1c088c 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -35,6 +35,10 @@
> > 
> >  #include <asm/kvm_host.h>
> > 
> > +#ifndef KVM_MAX_VCPU_ID
> > +#define KVM_MAX_VCPU_ID KVM_MAX_VCPUS  
> 
> As you are defining KVM_MAX_VCPU_ID in any case, would it make sense to
> provide the cap in generic code? power will simply override the value.
> 

I'll do that in v6. Thanks !

> > +#endif
> > +
> >  /*
> >   * The bit 16 ~ bit 31 of kvm_memory_region::flags are internally used
> >   * in kvm, other bits are visible for userspace which are defined in