linux-kernel - Re: [PATCH 3/6] KVM: x86/pmu: Use separate array for defining "PMU MSRs to save"

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Date:   Fri, 10 Feb 2023 21:23:35 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Aaron Lewis <aaronlewis@...gle.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Like Xu <likexu@...cent.com>
Subject: Re: [PATCH 3/6] KVM: x86/pmu: Use separate array for defining "PMU
 MSRs to save"

On Tue, Jan 24, 2023 at 11:49:02PM +0000, Sean Christopherson wrote:
> Move all potential to-be-saved PMU MSRs into a separate array so that a
> future patch can easily omit all PMU MSRs from the list when the PMU is
> disabled.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 153 ++++++++++++++++++++++++---------------------
>  1 file changed, 82 insertions(+), 71 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d4a610ffe2b8..9b6e1af63531 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1419,7 +1419,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
>   * may depend on host virtualization features rather than host cpu features.
>   */
>  
> -static const u32 msrs_to_save_all[] = {
> +static const u32 msrs_to_save_base[] = {

I guess the comments relating to msr_to_save_all should be updated as well. :)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 186cb6a81643..4bce96cd615e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1413,7 +1413,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
  *
  * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features)
  * extract the supported MSRs from the related const lists.
- * msrs_to_save is selected from the msrs_to_save_all to reflect the
+ * msrs_to_save is selected from the msrs_to_save_base to reflect the
  * capabilities of the host cpu. This capabilities test skips MSRs that are
  * kvm-specific. Those are put in emulated_msrs_all; filtering of emulated_msrs
  * may depend on host virtualization features rather than host cpu features.
@@ -1516,7 +1516,7 @@ static const u32 emulated_msrs_all[] = {
         * by arch/x86/kvm/vmx/nested.c based on CPUID or other MSRs.
         * We always support the "true" VMX control MSRs, even if the host
         * processor does not, so I am putting these registers here rather
-        * than in msrs_to_save_all.
+        * than in msrs_to_save_base.
         */
        MSR_IA32_VMX_BASIC,
        MSR_IA32_VMX_TRUE_PINBASED_CTLS,

For the comments of emulated_msrs_all, after renaming msrs_to_save_all to
msrs_to_save_base, maybe we do not need to take pains to explain that? 

B.R.
Yu