linux-kernel - Re: [PATCH v4 13/25] KVM: VMX: Check CPU_BASED_{INTR,NMI}_WINDOW_EXITING in setup_vmcs

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Message-ID: <YtnMzYztYVtRVV1B@google.com>
Date:   Thu, 21 Jul 2022 22:01:49 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 13/25] KVM: VMX: Check
 CPU_BASED_{INTR,NMI}_WINDOW_EXITING in setup_vmcs_config()

On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> CPU_BASED_{INTR,NMI}_WINDOW_EXITING controls are toggled dynamically by
> vmx_enable_{irq,nmi}_window, handle_interrupt_window(), handle_nmi_window()
> but setup_vmcs_config() doesn't check their existence. Add the check and
> filter the controls out in vmx_exec_control().
> 
> Note: KVM explicitly supports CPUs without VIRTUAL_NMIS and all these CPUs
> are supposedly lacking NMI_WINDOW_EXITING too. Adjust cpu_has_virtual_nmis()
> accordingly.
> 
> No functional change intended.
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---

Nit aside,

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

>  arch/x86/kvm/vmx/capabilities.h | 3 ++-
>  arch/x86/kvm/vmx/vmx.c          | 8 +++++++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index 069d8d298e1d..07e7492fe72a 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -82,7 +82,8 @@ static inline bool cpu_has_vmx_basic_inout(void)
>  
>  static inline bool cpu_has_virtual_nmis(void)
>  {
> -	return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS;
> +	return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS &&
> +		vmcs_config.cpu_based_exec_ctrl & CPU_BASED_NMI_WINDOW_EXITING;

I prefer to align these, though Paolo always scoffs at me :-)


static inline bool cpu_has_virtual_nmis(void)
{
	return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS &&
	       vmcs_config.cpu_based_exec_ctrl & CPU_BASED_NMI_WINDOW_EXITING;
}

>  }
>  
>  static inline bool cpu_has_vmx_preemption_timer(void)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 1aaec4d19e1b..ce54f13d8da1 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2487,10 +2487,12 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	      CPU_BASED_MWAIT_EXITING |
>  	      CPU_BASED_MONITOR_EXITING |
>  	      CPU_BASED_INVLPG_EXITING |
> -	      CPU_BASED_RDPMC_EXITING;
> +	      CPU_BASED_RDPMC_EXITING |
> +	      CPU_BASED_INTR_WINDOW_EXITING;
>  
>  	opt = CPU_BASED_TPR_SHADOW |
>  	      CPU_BASED_USE_MSR_BITMAPS |
> +	      CPU_BASED_NMI_WINDOW_EXITING |
>  	      CPU_BASED_ACTIVATE_SECONDARY_CONTROLS |
>  	      CPU_BASED_ACTIVATE_TERTIARY_CONTROLS;
>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PROCBASED_CTLS,
> @@ -4299,6 +4301,10 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
>  {
>  	u32 exec_control = vmcs_config.cpu_based_exec_ctrl;
>  
> +	/* INTR_WINDOW_EXITING and NMI_WINDOW_EXITING are toggled dynamically */
> +	exec_control &= ~(CPU_BASED_INTR_WINDOW_EXITING |
> +			  CPU_BASED_NMI_WINDOW_EXITING);
> +
>  	if (vmx->vcpu.arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)
>  		exec_control &= ~CPU_BASED_MOV_DR_EXITING;
>  
> -- 
> 2.35.3
>