On Tue, 16 Nov 2021 13:23:25 +0000, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: > > Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > > > On 11/12/21 15:02, Marc Zyngier wrote: > >>> I'd like KVM to be consistent across architectures and have the same > >>> (similar) meaning for KVM_CAP_NR_VCPUS. > >> Sure, but this is a pretty useless piece of information anyway. As > >> Andrew pointed out, the information is available somewhere else, and > >> all we need to do is to cap it to the number of supported vcpus, which > >> is effectively a KVM limitation. > >> > >> Also, we are talking about representing the architecture to userspace. > >> No amount of massaging is going to make an arm64 box look like an x86. > > > > Not sure what you mean? The API is about providing a piece of > > information independent of the architecture, while catering for a ppc > > weirdness. Yes it's mostly useless if you don't care about ppc, but > > it's not about making arm64 look like x86 or ppc; it's about not having > > to special case ppc in userspace. > > > > If anything, if KVM_CAP_NR_VCPUS returns the same for kvm and !kvm, then > > *that* is making an arm64 box look like an x86. On ARM the max vCPUs > > depends on VM's GIC configuration, so KVM_CAP_NR_VCPUS should take that > > into account. > > (I'm about to send v2 as we have s390 sorted out.) > > So what do we decide about ARM? [...] > - Always kvm_arm_default_max_vcpus to make the output independent on 'if > (kvm)'. This. Between two useless numbers, I prefer the one that doesn't introduce any userspace visible changes. Thanks, M. -- Without deviation from the norm, progress is not possible.
