linux-kernel - Re: [PATCH 2/2] kvm: rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU

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Message-ID: <YT+WpdnGodZE9krY@google.com>
Date:   Mon, 13 Sep 2021 18:21:25 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Eduardo Habkost <ehabkost@...hat.com>
Cc:     Juergen Gross <jgross@...e.com>, kvm@...r.kernel.org,
        x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Mackerras <paulus@...abs.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 2/2] kvm: rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU_IDS

On Mon, Sep 13, 2021, Eduardo Habkost wrote:
> On Mon, Sep 13, 2021 at 12:24 PM Sean Christopherson <seanjc@...gle.com> 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.