linux-kernel - Re: [PATCH v7 3/8] KVM: VMX: Detect Tertiary VM-Execution control when setup VMCS config

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Message-ID: <YkYuDo3hOmcwA1iF@google.com>
Date:   Thu, 31 Mar 2022 22:41:18 +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 v7 3/8] KVM: VMX: Detect Tertiary VM-Execution control
 when setup VMCS config

On Fri, Mar 04, 2022, Zeng Guang wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index c569dc2b9192..8a5713d49635 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2422,6 +2422,21 @@ 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,

I slightly prefer controls64 over controls_64.  As usual, KVM is inconsistent as
a whole, but vmcs_read/write64 omit the underscore, so we can at least be somewhat
consistent within VMX.

> +					 u32 msr, u64 *result)
> +{
> +	u64 allowed1;
> +
> +	rdmsrl(msr, allowed1);
> +
> +	/* Ensure minimum (required) set of control bits are supported. */
> +	if (ctl_min & ~allowed1)

Eh, just drop @ctl_min.  Practically speaking, there is zero chance tertiary
controls or any other control of this nature will ever be mandatory.  Secondary
controls would fall into the same boat, but specifying min=0 allows it to share
helpers, so it's the lesser of evils.

With the error return gone, this can be

  static __init u64 adjust_vmx_controls64(u64 ctl_opt, u32 msr)
  {
	u64 allowed;

	rdmsrl(msr, allowed);

	return ctl_opt & allowed;
  }

Alternatively, we could take the control-to-modify directly and have no return,
but I like having the "u64 opt = ..." in the caller.