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Date:   Tue, 18 May 2021 15:42:34 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Xu, Like" <like.xu@intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, weijiang.yang@intel.com,
        Kan Liang <kan.liang@linux.intel.com>, ak@linux.intel.com,
        wei.w.wang@intel.com, eranian@google.com, liuxiangdong5@huawei.com,
        linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org,
        Luwei Kang <luwei.kang@intel.com>,
        Like Xu <like.xu@linux.intel.com>
Subject: Re: [PATCH v6 06/16] KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR
 emulation for extended PEBS
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On Tue, May 18, 2021 at 04:44:13PM +0800, Xu, Like wrote:
> Will adding the following comments help you ?
> 
> +/*
> + * Currently, the only caller of this function is the atomic_switch_perf_msrs().
> + * The host perf conext helps to prepare the values of the real hardware for
> + * a set of msrs that need to be switched atomically in a vmx transaction.
> + *
> + * For example, the pseudocode needed to add a new msr should look like:
> + *
> + * arr[(*nr)++] = (struct perf_guest_switch_msr){
> + *???? .msr = the hardware msr address,
> + *???? .host = the value the hardware has when it doesn't run a guest,
> + *???? .guest = the value the hardware has when it runs a guest,

So personally I think the .host and .guest naming is terrible here,
because both values are host values. But I don't know enough about virt
to know if there's accepted nomencature for this.

> + * };
> + *
> + * These values have nothing to do with the emulated values the guest sees
> + * when it uses {RD,WR}MSR, which should be handled in the KVM context.
> + */
> ?static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)

Yes, now at least one can understand wth this function does, even though
the actual naming is still horrible. Thanks!

Additionally, would it make sense to add a pointer to the KVM code that
does the emulation for each MSR listed in this function?