linux-kernel - Re: [PATCH 01/11] KVM: x86/pmu: Update comments for AMD gp counters

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Date:   Wed, 23 Feb 2022 11:50:25 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <likexu@...cent.com>
Subject: Re: [PATCH 01/11] KVM: x86/pmu: Update comments for AMD gp counters

On Mon, Feb 21, 2022 at 3:52 AM Like Xu <like.xu.linux@...il.com> wrote:
>
> From: Like Xu <likexu@...cent.com>
>
> The obsolete comment could more accurately state that AMD platforms
> have two base MSR addresses and two different maximum numbers
> for gp counters, depending on the X86_FEATURE_PERFCTR_CORE feature.
>
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/kvm/pmu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index b1a02993782b..c4692f0ff87e 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -34,7 +34,7 @@
>   *   However AMD doesn't support fixed-counters;
>   * - There are three types of index to access perf counters (PMC):
>   *     1. MSR (named msr): For example Intel has MSR_IA32_PERFCTRn and AMD
> - *        has MSR_K7_PERFCTRn.
> + *        has MSR_F15H_PERF_CTRn or MSR_K7_PERFCTRn.

"Or" sounds exclusive. Maybe it would be better to say:

has MSR_K7_PERFCTRn and, for families 15H and later,
MSR_F15H_PERF_CTRn, where MSR_F15H_PERF_CTR[0-3] are aliased to
MSR_K7_PERFCTRn.