linux-kernel - Re: [PATCH v3 24/25] KVM: VMX: Cache MSR_IA32_VMX_MISC in vmcs

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Date:   Tue, 12 Jul 2022 15:11:38 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 24/25] KVM: VMX: Cache MSR_IA32_VMX_MISC in
 vmcs_config

On Fri, 2022-07-08 at 16:42 +0200, Vitaly Kuznetsov wrote:
> Like other host VMX control MSRs, MSR_IA32_VMX_MISC can be cached in
> vmcs_config to avoid the need to re-read it later, e.g. from
> cpu_has_vmx_intel_pt() or cpu_has_vmx_shadow_vmcs().
> 
> No (real) functional change intended.
> 
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/capabilities.h | 11 +++--------
>  arch/x86/kvm/vmx/vmx.c          |  8 +++++---
>  2 files changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index 07e7492fe72a..07f7a9534211 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -65,6 +65,7 @@ struct vmcs_config {
>         u64 cpu_based_3rd_exec_ctrl;
>         u32 vmexit_ctrl;
>         u32 vmentry_ctrl;
> +       u64 misc;
>         struct nested_vmx_msrs nested;
>  };
>  extern struct vmcs_config vmcs_config;
> @@ -225,11 +226,8 @@ static inline bool cpu_has_vmx_vmfunc(void)
>  
>  static inline bool cpu_has_vmx_shadow_vmcs(void)
>  {
> -       u64 vmx_msr;
> -
>         /* check if the cpu supports writing r/o exit information fields */
> -       rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
> -       if (!(vmx_msr & MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS))
> +       if (!(vmcs_config.misc & MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS))
>                 return false;
>  
>         return vmcs_config.cpu_based_2nd_exec_ctrl &
> @@ -371,10 +369,7 @@ static inline bool cpu_has_vmx_invvpid_global(void)
>  
>  static inline bool cpu_has_vmx_intel_pt(void)
>  {
> -       u64 vmx_msr;
> -
> -       rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
> -       return (vmx_msr & MSR_IA32_VMX_MISC_INTEL_PT) &&
> +       return (vmcs_config.misc & MSR_IA32_VMX_MISC_INTEL_PT) &&
>                 (vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_PT_USE_GPA) &&
>                 (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_RTIT_CTL);
>  }
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 35285109856f..ab091758c437 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2479,6 +2479,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>         u64 _cpu_based_3rd_exec_control = 0;
>         u32 _vmexit_control = 0;
>         u32 _vmentry_control = 0;
> +       u64 misc_msr;
>         int i;
>  
>         /*
> @@ -2613,6 +2614,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>         if (((vmx_msr_high >> 18) & 15) != 6)
>                 return -EIO;
>  
> +       rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
> +
>         vmcs_conf->size = vmx_msr_high & 0x1fff;
>         vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
>  
> @@ -2624,6 +2627,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>         vmcs_conf->cpu_based_3rd_exec_ctrl = _cpu_based_3rd_exec_control;
>         vmcs_conf->vmexit_ctrl         = _vmexit_control;
>         vmcs_conf->vmentry_ctrl        = _vmentry_control;
> +       vmcs_conf->misc = misc_msr;
>  
>         return 0;
>  }
> @@ -8241,11 +8245,9 @@ static __init int hardware_setup(void)
>  
>         if (enable_preemption_timer) {
>                 u64 use_timer_freq = 5000ULL * 1000 * 1000;
> -               u64 vmx_msr;
>  
> -               rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
>                 cpu_preemption_timer_multi =
> -                       vmx_msr & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
> +                       vmcs_config.misc & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
>  
>                 if (tsc_khz)
>                         use_timer_freq = (u64)tsc_khz * 1000;


Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky