Re: [PATCH v1 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Borislav Petkov]

On Tue, Jun 01, 2021 at 07:21:28PM -0700, Kuppuswamy Sathyanarayanan wrote:
> Add CPU feature detection for Trusted Domain Extensions support.
> TDX feature adds capabilities to keep guest register state and
> memory isolated from hypervisor.
> 
> For TDX guest platforms, executing CPUID(0x21, 0) will return

I'm assuming that 0 is ECX?

> following values in EAX, EBX, ECX and EDX.
> 
> EAX:  Maximum sub-leaf number:  0
> EBX/EDX/ECX:  Vendor string:
> 
> EBX =  "Inte"
> EDX =  "lTDX"
> ECX =  "    "
> 
> So when above condition is true, set X86_FEATURE_TDX_GUEST
> feature cap bit
		 ^
		 Fullstop.

> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index ac37830ae941..dddc3a27cc8a 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -238,6 +238,7 @@
>  #define X86_FEATURE_VMW_VMMCALL		( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
>  #define X86_FEATURE_PVUNLOCK		( 8*32+20) /* "" PV unlock function */
>  #define X86_FEATURE_VCPUPREEMPT		( 8*32+21) /* "" PV vcpu_is_preempted function */
> +#define X86_FEATURE_TDX_GUEST		( 8*32+22) /* Trusted Domain Extensions Guest */

What's the name of the feature bit? "TDX guest"? Why not only
X86_FEATURE_TDX and then you can have "tdx" in cpuinfo?

>  
>  /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
>  #define X86_FEATURE_FSGSBASE		( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> new file mode 100644
> index 000000000000..679500e807f3
> --- /dev/null
> +++ b/arch/x86/include/asm/tdx.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2020 Intel Corporation */
> +#ifndef _ASM_X86_TDX_H
> +#define _ASM_X86_TDX_H
> +
> +#define TDX_CPUID_LEAF_ID	0x21
> +
> +#ifdef CONFIG_INTEL_TDX_GUEST
> +
> +#include <asm/cpufeature.h>

As before - put the include at the top.

> +void __init tdx_early_init(void);
> +
> +#else // !CONFIG_INTEL_TDX_GUEST

No need for that // - comment

> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> new file mode 100644
> index 000000000000..5b14b72e41c5
> --- /dev/null
> +++ b/arch/x86/kernel/tdx.c
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (C) 2020 Intel Corporation */
> +
> +#include <asm/tdx.h>
> +
> +static inline bool cpuid_has_tdx_guest(void)
> +{
> +	u32 eax, signature[3];

Shorten that array name to "sig" so that you don't have to break the
cpuid_count() line below.

> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID)
> +		return false;
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &signature[0],
> +		    &signature[1], &signature[2]);
> +
> +	if (memcmp("IntelTDX    ", signature, 12))
> +		return false;
> +
> +	return true;

or simply:

return !memcmp(...

> +}
> +
> +void __init tdx_early_init(void)
> +{
> +	if (!cpuid_has_tdx_guest())
> +		return;
> +
> +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> +
> +	pr_info("TDX guest is initialized\n");

Use pr_fmt in this file:

#undef pr_fmt
#define pr_fmt(fmt)     "x86/tdx: " fmt

and then do

	pr_info("Guest initialized\n");

Thx.

-- 
Regards/Gruss,
    Boris.

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