linux-kernel - Re: [PATCH 1/6] x86/feat_ctl: Add new VMX feature, Tertiary VM-Execution control

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Date:   Mon, 2 Aug 2021 16:20:24 +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" <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 1/6] x86/feat_ctl: Add new VMX feature, Tertiary
 VM-Execution control

On Mon, Aug 02, 2021, Zeng Guang wrote:
> On 7/29/2021 7:44 AM, Sean Christopherson wrote:
> > On Fri, Jul 16, 2021, Zeng Guang wrote:
> > > @@ -42,6 +44,13 @@ static void init_vmx_capabilities(struct cpuinfo_x86 *c)
> > >   	rdmsr_safe(MSR_IA32_VMX_PROCBASED_CTLS2, &ign, &supported);
> > >   	c->vmx_capability[SECONDARY_CTLS] = supported;
> > > +	/*
> > > +	 * For tertiary execution controls MSR, it's actually a 64bit allowed-1.
> > > +	 */
> > > +	rdmsr_safe(MSR_IA32_VMX_PROCBASED_CTLS3, &ign, &supported);
> > > +	c->vmx_capability[TERTIARY_CTLS_LOW] = ign;
> > > +	c->vmx_capability[TERTIARY_CTLS_HIGH] = supported;
> > Assuming only the lower 32 bits are going to be used for the near future (next
> > few years), what about defining just TERTIARY_CTLS_LOW and then doing:
> > 
> > 	/*
> > 	 * Tertiary controls are 64-bit allowed-1, so unlikely other MSRs, the
> > 	 * upper bits are ignored (because they're not used, yet...).
> > 	 */
> > 	rdmsr_safe(MSR_IA32_VMX_PROCBASED_CTLS3, &supported, &ign);
> > 	c->vmx_capability[TERTIARY_CTLS_LOW] = supported;
> > 
> > I.e. punt the ugliness issue down the road a few years.
> Prefer to keep it complete, and use new variables like low/high consistent
> with its function meaning. Ok for that ?

Ya, either way works.