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

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Message-ID: <20d46894-a42f-88fc-124b-9d6662c57bef@redhat.com>
Date:   Thu, 29 Jul 2021 17:56:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Zeng Guang <guang.zeng@...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,
        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 1/6] x86/feat_ctl: Add new VMX feature, Tertiary
 VM-Execution control

On 29/07/21 01:44, Sean Christopherson wrote:
>> +	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.
> 

Or use two new variables low/high instead of supported/ign.

Paolo