linux-kernel - Re: [PATCH 4/4] KVM: VMX: Add a helper and macros to reduce boilerplate for sec exec ctls

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Date:   Wed, 23 Sep 2020 19:20:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] KVM: VMX: Add a helper and macros to reduce
 boilerplate for sec exec ctls

On 23/09/20 18:50, Sean Christopherson wrote:
> Add a helper function and several wrapping macros to consolidate the
> copy-paste code in vmx_compute_secondary_exec_control() for adjusting
> controls that are dependent on guest CPUID bits.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 128 +++++++++++++----------------------------
>  1 file changed, 41 insertions(+), 87 deletions(-)

The diffstat is enticing but the code a little less so...  Can you just
add documentation above vmx_adjust_secondary_exec_control that explains
the how/why?

Paolo

> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 5180529f6531..b786cfb74f4f 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4073,6 +4073,38 @@ u32 vmx_exec_control(struct vcpu_vmx *vmx)
>  }
>  
>  
> +static inline void
> +vmx_adjust_secondary_exec_control(struct vcpu_vmx *vmx, u32 *exec_control,
> +				  u32 control, bool enabled, bool exiting)
> +{
> +	if (enabled == exiting)
> +		*exec_control &= ~control;
> +	if (nested) {
> +		if (enabled)
> +			vmx->nested.msrs.secondary_ctls_high |= control;
> +		else
> +			vmx->nested.msrs.secondary_ctls_high &= ~control;
> +	}
> +}
> +
> +#define vmx_adjust_sec_exec_control(vmx, exec_control, name, feat_name, ctrl_name, exiting) \
> +({									 \
> +	bool __enabled;							 \
> +									 \
> +	if (cpu_has_vmx_##name()) {					 \
> +		__enabled = guest_cpuid_has(&(vmx)->vcpu,		 \
> +					    X86_FEATURE_##feat_name);	 \
> +		vmx_adjust_secondary_exec_control(vmx, exec_control,	 \
> +			SECONDARY_EXEC_##ctrl_name, __enabled, exiting); \
> +	}								 \
> +})
> +
> +#define vmx_adjust_sec_exec_feature(vmx, exec_control, lname, uname) \
> +	vmx_adjust_sec_exec_control(vmx, exec_control, lname, uname, ENABLE_##uname, false)
> +
> +#define vmx_adjust_sec_exec_exiting(vmx, exec_control, lname, uname) \
> +	vmx_adjust_sec_exec_control(vmx, exec_control, lname, uname, uname##_EXITING, true)
> +
>  static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>  {