On Mon, Sep 13, 2021, Juergen Gross wrote:
> KVM_MAX_VCPU_ID is not specifying the highest allowed vcpu-id, but the
> number of allowed vcpu-ids. This has already led to confusion, so
> rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU_IDS to make its semantics more
> clear
My hesitation with this rename is that the max _number_ of IDs is not the same
thing as the max allowed ID. E.g. on x86, given a capability that enumerates the
max number of IDs, I would expect to be able to create vCPUs with arbitrary 32-bit
x2APIC IDs so long as the total number of IDs is below the max.
On Mon, Sep 13, 2021 at 12:24 PM Sean Christopherson <[email protected]> wrote:
>
> On Mon, Sep 13, 2021, Juergen Gross wrote:
> > KVM_MAX_VCPU_ID is not specifying the highest allowed vcpu-id, but the
> > number of allowed vcpu-ids. This has already led to confusion, so
> > rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU_IDS to make its semantics more
> > clear
>
> My hesitation with this rename is that the max _number_ of IDs is not the same
> thing as the max allowed ID. E.g. on x86, given a capability that enumerates the
> max number of IDs, I would expect to be able to create vCPUs with arbitrary 32-bit
> x2APIC IDs so long as the total number of IDs is below the max.
>
What name would you suggest instead? KVM_VCPU_ID_LIMIT, maybe?
I'm assuming we are not going to redefine KVM_MAX_VCPU_ID to be an
inclusive limit.
--
Eduardo
On Mon, Sep 13, 2021, Eduardo Habkost wrote:
> On Mon, Sep 13, 2021 at 12:24 PM Sean Christopherson <[email protected]> wrote:
> >
> > On Mon, Sep 13, 2021, Juergen Gross wrote:
> > > KVM_MAX_VCPU_ID is not specifying the highest allowed vcpu-id, but the
> > > number of allowed vcpu-ids. This has already led to confusion, so
> > > rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU_IDS to make its semantics more
> > > clear
> >
> > My hesitation with this rename is that the max _number_ of IDs is not the same
> > thing as the max allowed ID. E.g. on x86, given a capability that enumerates the
> > max number of IDs, I would expect to be able to create vCPUs with arbitrary 32-bit
> > x2APIC IDs so long as the total number of IDs is below the max.
> >
>
> What name would you suggest instead? KVM_VCPU_ID_LIMIT, maybe?
>
> I'm assuming we are not going to redefine KVM_MAX_VCPU_ID to be an
> inclusive limit.
Heh, I haven't been able to come up with one, which is why I suggested the route
of making it an inclusive value internally within KVM.