linux-kernel - Re: [PATCH v4 3/6] KVM: VMX: Detect Tertiary VM-Execution control when setup VMCS config

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Date:   Fri, 10 Sep 2021 21:35:55 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Zeng Guang <guang.zeng@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kim Phillips <kim.phillips@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Kai Huang <kai.huang@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Robert Hu <robert.hu@...el.com>,
        Gao Chao <chao.gao@...el.com>,
        Robert Hoo <robert.hu@...ux.intel.com>
Subject: Re: [PATCH v4 3/6] KVM: VMX: Detect Tertiary VM-Execution control
 when setup VMCS config

On Mon, Aug 09, 2021, Zeng Guang wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 927a552393b9..ee8c5664dc95 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2391,6 +2391,23 @@ static __init int adjust_vmx_controls(u32 ctl_min, u32 ctl_opt,
>  	return 0;
>  }
>  
> +static __init int adjust_vmx_controls_64(u64 ctl_min, u64 ctl_opt,
> +					 u32 msr, u64 *result)
> +{
> +	u64 vmx_msr;
> +	u64 ctl = ctl_min | ctl_opt;
> +
> +	rdmsrl(msr, vmx_msr);
> +	ctl &= vmx_msr; /* bit == 1 means it can be set */
> +
> +	/* Ensure minimum (required) set of control bits are supported. */
> +	if (ctl_min & ~ctl)
> +		return -EIO;
> +
> +	*result = ctl;
> +	return 0;
> +}

More succinctly, since we don't need to force-set bits in the final value:

	u64 allowed1;

	rdmsrl(msr, allowed1);

	/* Ensure minimum (required) set of control bits are supported. */
	if (ctl_min & ~allowed1)
		return -EIO;

	*result = (ctl_min | ctl_opt) & allowed1;
	return 0;

>  static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  				    struct vmx_capability *vmx_cap)
>  {