linux-kernel - Re: [PATCH v4 2/6] KVM: x86: Introduce CPUID_8000_0007

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Message-ID: <CALMp9eSVQSMKbYKr0n-t3JP58hLGA8ZHJZAX34-E4YWUa+VYHA@mail.gmail.com>
Date:   Thu, 22 Sep 2022 10:09:08 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/6] KVM: x86: Introduce CPUID_8000_0007_EDX
 'scattered' leaf

Why do we need a new 'scattered' leaf? We are only using two bits in
the first one, right? And now we're only going to use one bit in the
second one?

I thought the point of the 'scattered' leaves was to collect a bunch
of feature bits from different CPUID leaves in a single feature word.

Allocating a new feature word for one or two bits seems extravagant.