linux-kernel - Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

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Message-ID: <20211005210423.yfftpxxmj3cjprtv@treble>
Date:   Tue, 5 Oct 2021 14:04:23 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

On Mon, Oct 04, 2021 at 07:51:57PM -0700, Kuppuswamy Sathyanarayanan wrote:
> @@ -495,6 +496,13 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  
>  	copy_bootdata(__va(real_mode_data));
>  
> +	/*
> +	 * tdx_early_init() has dependency on command line parameters.
> +	 * So the order of calling it should be after copy_bootdata()
> +	 * (in which command line parameter is initialized).
> +	 */
> +	tdx_early_init();

Which cmdline parameters are those?

> +/*
> + * Allocate it in the data region to avoid zeroing it during
> + * BSS initialization. It is mainly used in cc_platform_has()
> + * call during early boot call.
> + */
> +u64 __section(".data") is_tdx_guest = 0;

Or you could just give it a -1 value here to avoid the section
annotation.  Not sure why it needs 64 bits, any reason it can't just be
bool?

> +
> +static void __init is_tdx_guest_init(void)
> +{
> +	u32 eax, sig[3];
> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) {
> +		is_tdx_guest = 0;
> +		return;
> +	}
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
> +
> +	is_tdx_guest = !memcmp("IntelTDX    ", sig, 12);
> +}
> +
> +void __init tdx_early_init(void)
> +{
> +	is_tdx_guest_init();
> +
> +	if (!is_tdx_guest)
> +		return;
> +
> +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> +
> +	pr_info("Guest initialized\n");
> +}

What's the point of having both 'is_tdx_guest' and
X86_FEATURE_TDX_GUEST?  Are they not redundant?

-- 
Josh