linux-kernel - Re: [PATCH 09/26] x86/tdx: Detect TDX at early kernel decompression time

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Date:   Fri, 7 Jan 2022 17:27:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/26] x86/tdx: Detect TDX at early kernel decompression
 time

On Tue, Dec 14, 2021 at 06:02:47PM +0300, Kirill A. Shutemov wrote:
> @@ -370,6 +370,14 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
>  	lines = boot_params->screen_info.orig_video_lines;
>  	cols = boot_params->screen_info.orig_video_cols;
>  
> +	/*
> +	 * Detect if we are running in TDX guest environment.

Please use passive voice: no "we" or "I", etc,

> +	 *
> +	 * It has to be done before console_init() to use paravirtualized
						  ^
						  in order

...

> +void early_tdx_detect(void)
> +{
> +	u32 eax, sig[3];
> +
> +	if (cpuid_max_leaf() < TDX_CPUID_LEAF_ID)

What's the use of that helper?

AFAICT, none because you call cpuid_count below anyway. And you use that
helper only here.

IOW, you can simply use cpuid_count() and not add it.

> +		return;
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2],  &sig[1]);
> +
> +	if (memcmp(TDX_IDENT, sig, 12))
> +		return;
> +
> +	/* Cache TDX guest feature status */
> +	tdx_guest_detected = true;
> +}

...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette