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

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Message-ID: <1c6ad344-299c-bd78-c6e7-79a815e15ef1@intel.com>
Date:   Sat, 2 Apr 2022 20:58:38 +0800
From:   Zeng Guang <guang.zeng@...el.com>
To:     Sean Christopherson <seanjc@...gle.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" <kvm@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Luck, Tony" <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>,
        "Huang, Kai" <kai.huang@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hu, Robert" <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 4/1/2022 6:41 AM, Sean Christopherson wrote:
> 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;
>    }

Make sense. I will change it.  Thanks.


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