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

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Date:   Wed, 28 Jul 2021 23:44:41 +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 1/6] x86/feat_ctl: Add new VMX feature, Tertiary
 VM-Execution control

On Fri, Jul 16, 2021, Zeng Guang wrote:
> From: Robert Hoo <robert.hu@...ux.intel.com>
> 
> New VMX capability MSR IA32_VMX_PROCBASED_CTLS3 conresponse to this new
> VM-Execution control field. And it is 64bit allow-1 semantics, not like
> previous capability MSRs 32bit allow-0 and 32bit allow-1. So with Tertiary
> VM-Execution control field introduced, 2 vmx_feature leaves are introduced,
> TERTIARY_CTLS_LOW and TERTIARY_CTLS_HIGH.

...

>  /*
>   * Note: If the comment begins with a quoted string, that string is used
> @@ -43,6 +43,7 @@
>  #define VMX_FEATURE_RDTSC_EXITING	( 1*32+ 12) /* "" VM-Exit on RDTSC */
>  #define VMX_FEATURE_CR3_LOAD_EXITING	( 1*32+ 15) /* "" VM-Exit on writes to CR3 */
>  #define VMX_FEATURE_CR3_STORE_EXITING	( 1*32+ 16) /* "" VM-Exit on reads from CR3 */
> +#define VMX_FEATURE_TER_CONTROLS	(1*32 + 17) /* "" Enable Tertiary VM-Execution Controls */

Maybe spell out TERTIARY?   SEC_CONTROLS is at least somewhat guessable, I doubt
TERTIARY is the first thing that comes to mind for most people when seeing "TER" :-)

>  #define VMX_FEATURE_CR8_LOAD_EXITING	( 1*32+ 19) /* "" VM-Exit on writes to CR8 */
>  #define VMX_FEATURE_CR8_STORE_EXITING	( 1*32+ 20) /* "" VM-Exit on reads from CR8 */
>  #define VMX_FEATURE_VIRTUAL_TPR		( 1*32+ 21) /* "vtpr" TPR virtualization, a.k.a. TPR shadow */
> diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
> index da696eb4821a..2e0272d127e4 100644
> --- a/arch/x86/kernel/cpu/feat_ctl.c
> +++ b/arch/x86/kernel/cpu/feat_ctl.c
> @@ -15,6 +15,8 @@ enum vmx_feature_leafs {
>  	MISC_FEATURES = 0,
>  	PRIMARY_CTLS,
>  	SECONDARY_CTLS,
> +	TERTIARY_CTLS_LOW,
> +	TERTIARY_CTLS_HIGH,
>  	NR_VMX_FEATURE_WORDS,
>  };
>  
> @@ -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.

> +
>  	rdmsr(MSR_IA32_VMX_PINBASED_CTLS, ign, supported);
>  	rdmsr_safe(MSR_IA32_VMX_VMFUNC, &ign, &funcs);
>  
> -- 
> 2.25.1
>