linux-kernel - Re: [PATCH v4 18/25] KVM: VMX: Add missing CPU based VM execution controls to vmcs

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Date:   Thu, 21 Jul 2022 22:39:00 +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 18/25] KVM: VMX: Add missing CPU based VM execution
 controls to vmcs_config

On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> As a preparation to reusing the result of setup_vmcs_config() in
> nested VMX MSR setup, add the CPU based VM execution controls which KVM
> doesn't use but supports for nVMX to KVM_OPT_VMX_CPU_BASED_VM_EXEC_CONTROL
> and filter them out in vmx_exec_control().
> 
> No functional change intended.
> 
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 6 ++++++
>  arch/x86/kvm/vmx/vmx.h | 6 +++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 2fb89bdcbbd8..9771c771c8f5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4240,6 +4240,12 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
>  {
>  	u32 exec_control = vmcs_config.cpu_based_exec_ctrl;
>  
> +	/* Not used by KVM but supported for nesting. */

And then for this one, clarify that these _are_ enabled in vmcs02.  It doesn't
really matter, I was just surprised by the "SAVE_PAT" in the previous patch because
for a second I thought we were leaking host state :-)

	/*
	 * Not used by KVM, but fully supported for nesting, i.e. are allowed in
	 * vmcs12 and propagated to vmcs02 when set in vmcs12.
	 */

> +	exec_control &= ~(CPU_BASED_RDTSC_EXITING |
> +			  CPU_BASED_USE_IO_BITMAPS |
> +			  CPU_BASED_MONITOR_TRAP_FLAG |
> +			  CPU_BASED_PAUSE_EXITING);
> +
>  	/* INTR_WINDOW_EXITING and NMI_WINDOW_EXITING are toggled dynamically */
>  	exec_control &= ~(CPU_BASED_INTR_WINDOW_EXITING |
>  			  CPU_BASED_NMI_WINDOW_EXITING);
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index e9c392398f1b..758f80c41beb 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -539,9 +539,13 @@ static inline u8 vmx_get_rvi(void)
>  #endif
>  
>  #define KVM_OPT_VMX_CPU_BASED_VM_EXEC_CONTROL			\
> -	(CPU_BASED_TPR_SHADOW |					\
> +	(CPU_BASED_RDTSC_EXITING |				\
> +	CPU_BASED_TPR_SHADOW |					\
> +	CPU_BASED_USE_IO_BITMAPS |				\
> +	CPU_BASED_MONITOR_TRAP_FLAG |				\
>  	CPU_BASED_USE_MSR_BITMAPS |				\
>  	CPU_BASED_NMI_WINDOW_EXITING |				\
> +	CPU_BASED_PAUSE_EXITING |				\
>  	CPU_BASED_ACTIVATE_SECONDARY_CONTROLS |			\
>  	CPU_BASED_ACTIVATE_TERTIARY_CONTROLS)
>  
> -- 
> 2.35.3
>