linux-kernel - Re: [PATCHv2 09/29] x86/tdx: Detect TDX at early kernel decompression time

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Date:   Tue, 1 Feb 2022 19:30:52 +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: [PATCHv2 09/29] x86/tdx: Detect TDX at early kernel
 decompression time

On Mon, Jan 24, 2022 at 06:01:55PM +0300, Kirill A. Shutemov wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> The early decompression code does port I/O for its console output. But,
> handling the decompression-time port I/O demands a different approach
> from normal runtime because the IDT required to support #VE based port
> I/O emulation is not yet set up. Paravirtualizing I/O calls during
> the decompression step is acceptable because the decompression code size is
> small enough and hence patching it will not bloat the image size a lot.
> 
> To support port I/O in decompression code, TDX must be detected before
> the decompression code might do port I/O. Add support to detect for
> TDX guest support before console_init() in the extract_kernel().

s/Add support to detect for TDX guest support before console_init() in the extract_kernel()./Detect whether the kernel runs in a TDX guest./

Simple.

> Detecting it above the console_init() is early enough for patching
> port I/O.

No need for that sentence - there's already a comment above the call
below.

> 
> Add an early_is_tdx_guest() interface to get the cached TDX guest

s/get/query/

> status in the decompression code.

...

> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index a4339cb2d247..d8373d766672 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -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 TDX guest environment.
> +	 *
> +	 * It has to be done before console_init() in order to use
> +	 * paravirtualized port I/O oprations if needed.

Unknown word [oprations] in comment.
Suggestions: ['orations', 'operations', 'op rations', 'op-rations', 'preparations', 'reparations', 'inspirations', 'operation']

> +	 */
> +	early_tdx_detect();
> +
>  	console_init();
>  
>  	/*

...

> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> new file mode 100644
> index 000000000000..12bede46d048
> --- /dev/null
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -0,0 +1,7 @@
> +#ifndef _ASM_X86_SHARED_TDX_H
> +#define _ASM_X86_SHARED_TDX_H

WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
#232: FILE: arch/x86/include/asm/shared/tdx.h:1:
+#ifndef _ASM_X86_SHARED_TDX_H

Why isn't checkpatch part of your patch creation workflow?

> +
> +#define TDX_CPUID_LEAF_ID	0x21
> +#define TDX_IDENT		"IntelTDX    "
> +
> +#endif
	  ^
	 /* _ASM_X86_SHARED_TDX_H */

-- 
Regards/Gruss,
    Boris.

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