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

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Date:   Mon, 13 Sep 2021 16:24:11 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     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>,
        Eduardo Habkost <ehabkost@...hat.com>
Subject: Re: [PATCH 2/2] kvm: rename KVM_MAX_VCPU_ID to KVM_MAX_VCPU_IDS

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.